Arsene Wenger says he feared for his 'fatigued' players when Arsenal conceded a penalty in Sunday's 3-0 Premier League win against Watford.
Ainsley Maitland-Niles brought down Roberto Pereyra with the hosts leading 2-0 at Emirates Stadium, but Troy Deeney's effort was superbly saved by Petr Cech before Henrikh Mkhitaryan added to earlier goals from Shkodran Mustafi and Pierre Emerick-Aubameyang to wrap up the win.
Deeney had questioned Arsenal's "cojones" following their 2-1 defeat at Vicarage Road earlier in the season, making Cech's save - his first from a spot-kick since 2011 - all the sweeter for the home side, who snapped a three-game losing streak in the top flight.
The result also brought up Wenger's 700th win as Gunners boss, but the Frenchman conceded the three points could have been in doubt had Deeney found the net.
"It was a difficult game like you get in the Premier League," he told BBC Sport. "But overall the spirit and desire was good.
"The spirit kept us out of trouble. We dealt well with set-pieces, which is why they could not come back.
"At 2-0 they had a penalty and if they come back to 2-1 it is a fact we have a bit of fatigue and we could have been in trouble, but we took advantage of that and you have to give credit to the players, they stuck together and of course a great penalty save."
Wenger rested Aaron Ramsey and Laurent Koscielny as he prepares to welcome AC Milan to north London for the second leg of a Europa League last-16 tie Arsenal lead 2-0 following Thursday's initial clash at San Siro.
"I selected my team to have the chance to win the game and also rest some players I did not want to get injured," he added.
"Because we are not so far to the end of the season, so any injuries you lose them for the rest of the season."