The two promotion hopefuls will renew hostilities at Somerset Park on Friday evening, with hosts needing a big turnaround in order to reach the final.
Match preview
Despite registering 11 shots while enjoying the lion's share of possession in the first leg, Ayr United suffered a damaging defeat at Firhill Stadium, handing Partick Thistle a significant advantage in the process.
After finishing second in the Scottish Championship table - one point above Partick - the Honest Men skipped the playoff quarter-finals and headed straight into the semi-finals, but they were humbled by the Jags last week.
Lee Bullen's men carried a five-game unbeaten streak into the first leg, having ended the regular season with a run of two wins and three draws to give their fans plenty of reasons for optimism ahead of the playoffs.
However, Ayr United must now score three unanswered goals to stand any chance of reaching the final, and they have scored three goals in just one of their last 11 home league games, with two goals coming in their previous three.
After finishing fourth in the standings, Partick Thistle made light work of Queen's Park in the playoff quarter-finals, scoring four goals in both legs to chalk up an 8-3 aggregate victory over the team that finished third.
Veteran striker Brian Graham scored in both matches against Queen's Park, and the 35-year-old was again the star of the show in the semi-final first leg as he bagged a second-half brace to build on Jack McMillan's opener.
Although Ayr United dominated the ball last time out, the Jags managed to rack up 19 shots - six of which were on target - while the visitors squandered numerous goalscoring opportunities at Firhill Stadium.
Not only have Kris Doolan's men avoided defeat in each of their last eight matches, but they have also avoided defeat in 14 of their previous 15, so they will be confident of booking their place in the final on Friday.
Ayr United Scottish Premiership Playoffs form:
L
Ayr United form (all competitions):
D
D
D
W
W
L
Partick Thistle Scottish Premiership Playoffs form:
W
W
W
Partick Thistle form (all competitions):
D
W
D
W
W
W
Team News
Ayr United will be hoping that star striker Dipo Akinyemi is fit to face Partick on Friday after the PFA Scotland Championship Player of the Year missed the first leg.
Akinyemi has notched 24 goals and 11 assists in 44 appearances across all competitions this season, although Mark McKenzie could lead the line again if Akinyemi misses out.
Having contributed nine goals from midfield this term, Ben Dempsey will continue alongside Andy Murdoch in the Honest Men's engine room, with Josh Mullin and Daire O'Connor operating on the wings.
As for Partick Thistle, they look set to be without midfielder Stuart Bannigan on Friday after the 30-year-old picked up an injury in the first leg of the playoff quarter-finals.
Brian Graham will continue to lead the line for the Jags, having netted 21 goals this term, including four in three playoff matches, while Steven Lawless, Scott Tiffoney and Aidan Fitzpatrick are expected to support the lone striker.
At the opposite end of the pitch, goalkeeper David Mitchell will go in search of his 11th clean sheet of the campaign after achieving eight shutouts in the last 13 games.
Ayr United possible starting lineup:
Albinson; Hewitt, Musonda, McGinty, Reading; Dempsey, Murdoch; O'Connor, Maguire, Mullin; McKenzie
Partick Thistle possible starting lineup:
Mitchell; McMillan, Muirhead, Brownlie, Holt; Turner, Docherty; Lawless, Tiffoney, Fitzpatrick; Graham
We say: Ayr United 2-1 Partick Thistle
With a three-goal deficit to overturn, Ayr United have no choice but to go for broke on Friday, but the hosts will find it difficult to recover from their first-leg failures.