Bouazza (centre) scored the eventual winner
Watford scraped into the semi-finals of the FA Cup but were made to work for their progress by a valiant Plymouth.
Hamuer Bouazza powered in a left-foot shot to put the visitors ahead but the goal galvanised Plymouth.
Watford keeper Ben Foster palmed away a Kevin Gallen free-kick and denied Sylvan Ebanks-Blake when one-on-one as Plymouth created plenty of chances.
But they were frustrated by Foster and their lack of a finishing touch as they bowed out of the competition.
The fervour of the Home Park crowd and the romance of the tie, combined with the reward for the winner, appeared to have affected both sets of players early on.
Plymouth's towering centre-back Krisztian Timar caught Watford striker Steve Kabba with a stray arm and the home side had to be especially wary of letting the occasion get to them.
The Championship outfit suffered a blow when they allowed Bouazza to run on to a low Kabba cross and shoot home from just inside the box.
The agony of missed chances shows for Plymouth
But the setback seemed to give Plymouth focus and they mounted a spell of sustained pressure that led to them being denied on several occasions.
David Norris latched on to a Kevin Gallen ball to the near post and, instead of shooting, overran the ball as he tried to take it around keeper Foster.
A Scott Sinclair strike was blocked by Danny Shittu and Lilian Nalis volleyed agonisingly over before Foster palmed a Gallen free-kick just wide at full stretch.
Ebanks-Blake had an angled shot saved by the busy Foster as Watford were again indebted to their England keeper.
The tie should have then been level when Paul Connolly fizzed in a low cross across goal but both Gallen and Ebanks-Blake failed to get the telling touch.
Plymouth continued to strive for a deserved equaliser and Norris sent an angled drive high as his miss epitomised his side's profligacy and Foster's form.
Foster was again at full-stretch to keep out an effort from his team-mate Damien Francis, who diverted the ball goalwards from an attemped clearance. Watford may be battling against relegation from the Premiership but will go into the draw for the semi-finals of the FA Cup at 1330 GMT on Monday.
Plymouth: McCormick, Connolly, Seip, Timar, Sawyer (Halmosi 76), Gosling (Hayles 46), Norris, Nalis, Sinclair (Capaldi 76), Ebanks-Blake, Gallen.
Subs Not Used: Hodges, Summerfield.
Booked: Seip, Connolly.
Watford: Foster, Mariappa, Shittu, DeMerit, Powell, Smith, Francis, Mahon, Bouazza, Kabba (Chambers 59), Priskin (Henderson 73).
Subs Not Used: Lee, Doyley, Rinaldi.
Booked: Foster, Chambers.
Goals: Bouazza 21.
Ref: C Foy (Merseyside).