With Gastón Ramírez's 15th-minute stunner the highlight of dominant first half against the League 1 side, Saints were made to work hard for their victory after the break before Jos Hooiveld wrapped matters up with a header seven minutes from time.
"It was a tough game, a difficult game," admitted Pérez when speaking to Saints Player
"Sometimes in the cup games the opponent plays with a lot of speed, a lot of passion and they try to do their best playing in a nice stadium.
"At the end it was a difficult game – we won but it wasn’t easy. We did a lot of running so it was also good physical training and a good lesson for the future.
"In these types of games, when you are making a lot of changes, it is difficult for the players to adjust. In the end I think we learn a lot from these type of games."
While it was Gastón Ramírez and Jos Hooiveld who scored Saints' goals, Pérez had praise for Tadanari Lee on his return to first-team contention.
The forward was making his first senior start in almost a year, having spent time out on loan in his native Japan during the latter half of last season.
"He did very well," Pérez said of Lee's showing. "We were speaking on the bench about his performance, especially in the first half where he was very dynamic.
"He played not only as a forward but he tried to help the team link up by playing as a winger and in between the lines, so we are really happy with his performance."
The likes of Maya Yoshida, Jack Cork and Guly do Prado also had the chance to get minutes under their belts, while youngsters Harrison Reed and Omar Rowe came off the bench to make their home debuts.
And Pérez was happy with the blend of experience and youth that the management were able to call upon for the match.
"The principle objective for today was to give the professional players 90 minutes and give some minutes to the younger players at the end," he said.
"With the result you have to manage that situation, but we were able to give the young players like Omar and Harrison Reed a few minutes.
"You always need to play with intensity, but the youngsters offer the team a freshness to help with the physical performance so we are happy for all of them."