The home team ran out 5-0 winners against MK Dons in the previous round on August 13, while Wayne Rooney's Plymouth advanced after winning 3-0 and dominating proceedings against Cheltenham Town on the same date.
Match preview
The hosts' win against MK Dons was spearheaded by Thomas Ince, who managed to score a hat-trick and register an assist.
Matthew Pollock and Kwadwo Baah also scored on the night, and in truth, the scoreline did not flatter Watford.
The Hornets limited MK Dons to just three attempts inside the penalty area, while they themselves had 24 shots from 57% possession, 18 of which were from inside the box.
Tom Cleverley's side have started the Championship season in excellent form and are currently second in the table with nine points from their first three games.
Watford are also averaging the second most shots on target per match, while having created the third most big chances of any team in the division.
Watford are also averaging the second most shots on target per match, while having created the third most big chances of any team in the division.
Opponents Plymouth Argyle won in the first round of the EFL Cup thanks to goals from Ben Waine, Ryan Hardie and Mustapha Bundu.
The Greens were deserving victors considering they had 70% possession, produced 32 shots and limited their opponents to just three attempts inside the penalty area.
However, though they thoroughly outclassed Cheltenham Town, Plymouth are currently fourth last in the Championship in 21st place, with just two points from their opening three league games.
Their 4-0 loss on August 11 against Sheffield Wednesday in their first league match was followed up by consecutive 1-1 draws against Hull City and most recently Queens Park Rangers on August 24.
Rooney praised his side for their draw against QPR and applauded their character for managing to secure a draw despite Adam Forshaw being sent off in the 29th minute, as well as Freddie Issaka in the first minute of stoppage time at the end of the second half.
Watford EFL Cup form:
W
Watford form (all competitions):
Plymouth Argyle EFL Cup form:
W
Plymouth Argyle form (all competitions):
Team News
Watford will be without defender Wesley Hoedt as he has signed for Saudi Pro League side Al Shabab.
The hosts could start Ken Sema, Kwadwo Bahh and Ryan Porteous, who all featured from the bench in the Hornets win against Derby on August 24.
Meanwhile, the visitors will be unable to select both Freddie Issaka and Adam Forshaw, while Brendan Galloway was forced off against QPR due to injury.
Julio Pleguezuelo could replace Galloway in defence, and Michael Obafemi could be given a start after featuring from the bench against QPR.
Watford possible starting lineup:
Bachmann; Pollock, Sierralta, Porteous; Andrews, Sissoko, Dele-Bashiru, Sema; Baah, Chakvetadze; Rajovic
Plymouth Argyle possible starting lineup:
Hazard; Edwards, Gibson, Pleguezuelo, Mumba; Randell, Houghton; Obafemi, Gyabi, Whittaker; Hardie
We say: Watford 2-1 Plymouth Argyle
Plymouth have proven they are capable of being resilient defensively, but they could struggle on Tuesday given the energy exerted in their valiant draw against QPR.