Glen McAuley had fired the young Reds in front following a brilliant team move, and despite the Black Cats levelling the scores, Curtis Jones netted a last minute winner.
It was the perfect end to a great week for Gerrard’s squad after the U19 group clinched qualification for the last 16 of the UEFA Youth League following a 4-0 win over Sevilla in Spain.
Gerrard's charges also moved up to third place in the U18s Premier League, and are now just three points behind leaders Manchester City who visit Kirkby on Tuesday night.
"That’s our biggest win of the season, because of the week we’ve had and what we’ve got coming up, that’s the biggest win of the season," Gerrard told Liverpoolfc.com.
"It was about mentality and character. We did start flat, we weren’t at it, but we stuck at it. We were sloppy for their goal, we went to sleep at the back post, but credit to Sunderland, they’re a good team, one of the best teams we’ve played so far in the league so to get the win very late on against a good team after a busy week, I can’t be any more happy than that."
Gerrard was pleased with the character of his team and the way they kept battling for the victory against a well organised Sunderland.
He added: "We were much better second half, first half we were a bit flat, a bit sluggish.
"I expected it a little bit tonight after the travelling in midweek and obviously being on such a high with the Sevilla result.
"A lot of these lads were involved in that game, in the XI and the squad, so it doesn’t surprise me that we were a little bit off it, but second half I thought we were brilliant.
"We pinned them back, we had to find a way, they had a tight, narrow block, and to be fair to Sunderland they were a decent team, but credit to my boys, they found a way in the end.
"We could've made it a little bit earlier for my sake but I’m pleased with them, I can’t give them enough credit – after a long week, we’ve found a way to beat a decent team, so very pleased."
LFCTV GO: Watch highlights from the 2-1 win over Sunderland
With Manchester City visiting the Kirkby Academy on Tuesday night in a top-of-the-table clash in the U18s Premier League, Gerrard chose to rest key duo Liam Millar and Curtis Jones, who both started on the bench against Sunderland.
The pair were introduced in the second-half and they made a big impact with Jones netting the winner after Millar’s effort came back off the post.
Explaining his decision to start the duo on the bench, Gerrard said: "The way they play, they played in Sevilla and all they did was run, they run all day long with long-distance sprints and I was told before the game that they’re the two I need to look after.
"It was also an opportunity to give other players minutes. I can’t keep picking the same XI all year round, I’ve got to let other players grow, let them develop as well, so I was a little bit caught on my XI this time around.
"But of course I don’t want to see them two players on the bench, I want them in my XI, I want them to play, but they got 30-35 minutes and did the damage and got their teammates three very important points."