Supporters were still making their way up the steps by the time the Irishman breached the Hornets' net, and some may have ironically already departed the stadium before Andre Gray levelled the contest in the 90th minute.
Long's rapid-fire strike for the Saints broke a Premier League goal record that had stood for almost 19 years, and while the 37-year-old can still proudly lay claim to registering in record time in the Premier League, a new name took up residence in the silver medal position last season.
Here, Sports Mole runs down the 10 quickest goals in the history of the Premier League on the anniversary of Long's historic effort.
10. James Beattie - Chelsea vs. Southampton, April 2004 - 13.52 seconds
In what would prove to be his final half-season in a Southampton jersey, legendary Saints striker James Beattie kicked off the 2004-05 campaign with a bang, stunning would-be champions Chelsea at Stamford Bridge with just 13 seconds gone.
Joe Cole was the guilty party, playing a backwards pass straight into the feet of the Englishman, who had Ricardo Carvalho and John Terry in front of him some 35 yards from goal but let fly with an astonishing half-volley over Petr Cech's head.
Beattie's wonder strike would prove to be just a consolation, though, as Chelsea fought back to prevail 2-1 on the day, and the former England forward would only go on to score one more Premier League goal for the South Coast club before bidding farewell in January 2005.
9. Kevin Nolan - Blackburn vs. Bolton Wanderers January 2004 - 13.48 seconds
Seven goals flew into the back of the net during an engrossing Lancashire derby between Blackburn Rovers and Bolton Wanderers in January 2004, and Kevin Nolan's 13.48-second strike would be a sign of things to come at Ewood Park.
Martin Taylor unsuccessfully tried to see the ball out for an early goal kick, but Kevin Davies managed to steal in and prod the ball back into the danger area for the arriving Nolan, whose vicious first-time drive rippled the roof of the net.
The Englishman's strike preceded a phenomenal Blackburn fightback as Bolton fell 3-1 down, but there would be another outrageous twist to the tale as the Trotters ended up prevailing 4-3, with Nolan scoring both the first and last goals of the night.
8. Chris Sutton - Everton vs. Blackburn, April 1995- 12.94 seconds
One of 15 goals he struck during Blackburn's incredible 1994-95 Premier League-winning season, Chris Sutton needed just under 13 seconds to break the deadlock at Everton's Goodison Park home in April 1995, thanks to an aerial link-up with Alan Shearer.
Sutton won the first header from a long ball forward, before Shearer then nodded the ball back into his teammate's path, and the former did the rest; taking the ball forward with a neat touch before clinically finding the bottom corner.
Shearer would go on to notch one himself just six minutes later, and even through Graham Stuart halved the deficit towards the break with a long-range stunner, Rovers' early show was enough for all three points en route to Premier League glory.
7. Dwight Yorke - Coventry City vs. Aston Villa, September 1995 - 12.16 seconds
Before donning the Manchester United jersey and scoring for fun at Old Trafford, Dwight Yorke earned a slice of history with Aston Villa in 1995, scoring the quickest headed goal on record in the Premier League.
A trip to Coventry City saw Villa immediately surge down the right through Ian Taylor, who had time to pick out a cross to Yorke, and the former Trinidad and Tobago international directed a bullet header into the top corner.
Yorke's goal would seemingly be the only strike to separate the two sides on the day, but inside the final 10 minutes of normal time, Savo Milosevic wrapped up the win with a fine brace - his second goal was assisted by his strike partner.
6. Mark Viduka - Charlton Athletic vs. Leeds United, March 2001 - 11.90 seconds
In what was his first season in English football, former Leeds United striker Mark Viduka was best remembered for his fantastic four-goal haul against Liverpool, but the 48-year-old also scored the fastest goal of any non-European player in Premier League history.
During the business end of the 2000-01 season, Leeds took a trip to the Valley to meet Charlton Athletic, where Alan Smith headed a long ball down into the path of Viduka, who was criminally given acres of space to pick his spot and curl home into the bottom corner.
Smith would then go from provider to goalscorer to ensure a 2-1 win for the Whites after Shaun Bartlett had drawn the Addicks level, but Leeds' quest for another season in the Champions League would ultimately end in failure.
5. Christian Eriksen - Tottenham Hotspur vs. Manchester United, January 2018 - 10.54 seconds
Christian Eriksen may now be aiding Manchester United's efforts to find the back of the net, but during his Tottenham Hotspur heyday, the Dane once needed just 10-and-a-half seconds to breach the Red Devils' net in the 2017-18 season.
As has been the case with several goals on this list already, the goal was sparked by an attacker winning a header from a long ball over the top - this time Harry Kane flicked on Jan Vertonghen's hoofed pass - and even though Dele Alli's effort was blocked by Chris Smalling, the rebound fell kindly for Christian Eriksen to score.
The Lilywhites would go on to notch a second before the break courtesy of a Phil Jones own goal, and Eriksen's effort remains the quickest goal ever scored at the new Wembley Stadium, just a couple of seconds quicker than Ilkay Gundogan's FA Cup final opener last year.
4. Alan Shearer - Newcastle United vs. Manchester City, January 2003 - 10.52 seconds
Shearer's name has inevitably already been mentioned once on this list, albeit in an assisting capacity rather than a goalscoring one, but the Englishman's effort for Newcastle against Manchester City in January 2003 was the second-quickest goal ever scored in the Premier League for over 15 years.
Timed at just 0.02 seconds quicker than Eriksen's for Tottenham, Shearer charged down an attempted punt forward from City goalkeeper Carlo Nash, thereby giving himself an empty net to tap into.
In fact, Shearer's 10-second strike is still the quickest Premier League home goal on record, and with Kane currently smashing Bundesliga records for fun, the former's unrivalled tally of 260 strikes in the competition remains safe for now.
3. Ledley King - Bradford City vs. Tottenham, December 2000 - 9.82 seconds
While Kane was synonymous with spectacular goals for Tottenham Hotspur, former captain Ledley King - despite his legendary status - was less so, only managing 13 efforts in 322 matches for the Lilywhites.
However, one of those strikes stood as the quickest goal in Premier League history for over 18 years, as during a trip to Bradford City in December 2000, the centre-back picked up a loose ball in the middle of the park, casually sauntered forward and found the bottom corner with the aid of a deflection.
King's slightly fortuitous goal was the first to be scored in the Premier League before the 10-second mark, and the 43-year-old's iconic '26' shirt remains unofficially retired in his honour.
2. Philip Billing - Arsenal vs. Bournemouth, March 2023 - 9.11 seconds
Sticking with the North London theme, Stoke City goalkeeper Asmir Begovic was knocked out of the Premier League's 10 fastest goals in history at the Emirates last March, where Philip Billing forced his way into the podium places on this list thanks to an all-too familiar slow start from Arsenal.
Gary O'Neil's men dashed forward and overloaded the penalty area straight from kickoff in an attempt to catch Arsenal out, and it proved to be a genius move from the Cherries, as Dango Ouattara's low cross somehow evaded a sea of red shirts and fell at the feet of Billing, who could not miss from a few yards out.
The Dane's 9.11-second finish officially became the second-fastest goal the competition has ever seen, but the afternoon ended in abject excruciation for Bournemouth, as Reiss Nelson's spectacular injury-time winner completed a monumental Arsenal comeback.
1. Shane Long - Watford vs. Southampton, April 2019 - 7.69 seconds
Shane Long enjoyed one last jaunt at Reading before hanging up his boots at the end of last season, but the 37-year-old can rest easy knowing that his remarkable Premier League record should not come under threat for some time.
Reinstated to the Southampton starting lineup for a trip to Watford in April 2019, Long took a lesson out of the Shearer playbook by charging down a clearance - this one from Hornets defender Craig Cathcart - and after the ball bounced off his backside, he comfortably shrugged off a desperate Cathcart and lifted the ball over Ben Foster with exemplary composure.
The Irishman's 7.69-second opener at Vicarage Road knocked King off his Premier League fastest goals perch, and while the Saints would then succumb to a 90th-minute Gray equaliser, Long departed with his name etched into footballing folklore.