He hadn't played since tearing a ligament in his foot in the pre-season game at Morecambe earlier this month, and admitted the pace caught up with him in the second half.
Fitness
But the 31-year-old intends to step up his fitness this week – perhaps even in the reserves against Manchester City tomorrow night – ahead of Ireland's crunch World Cup qualifier against France in Dublin next Wednesday.
Kavanagh told the Evening Post: "It was great to be back on Saturday although it was hard work because I'd only played one 90-minute game in pre-season.
"I got 70 minutes under my belt against Sunderland and the fitness will get stronger.
"The victory and clean sheet were so important and it gets that particular monkey off our back.
"It will give us that little bit more confidence and sets us up nicely for the next games after the international break."
Kavanagh didn't think he would miss the opening two games of the season when he first suffered the foot injury.
"I landed awkwardly on my heel after taking a shot and I just thought I had bruised it," said the former Cardiff player.
"It turned out I had ripped the ligament in my foot so it was disappointing.
"Of course it was very frustrating having to watch the first couple of games from the sidelines, and I was delighted to be able to contribute again on Saturday.
"Perhaps I wasn't too impressive with my fitness, but I have been out for four weeks and it takes times to get your sharpness back.
"I'll work on my fitness this week – I might ask to play in the reserves tomorrow – and that should improve it.
"The Ireland squad doesn't meet up until Friday morning ready for the game against France next week.
"We've three games left in our group, against France and Switzerland at home, and Cyprus away, and if we win them all we qualify."
Latics manager Paul Jewell was pleased to see the return of Kavanagh against Sunderland, and of Lee McCulloch.
It gave him more selection options after being down to his last 16 fit players at Charlton the week before.
However, McCulloch last night pulled out of the Scotland squad for their World Cup qualifiers against Italy and Norway to rest the knee injury which kept him out of action at the start of the season.
The 27-year-old only played against Sunderland with the help of three painkilling injections before kick-off.
Leighton Baines has got a late call-up for the England Under-21 squad, joining Ryan Taylor in Peter Taylor's party.
Meanwhile, Jewell hopes he'll have even more bodies available before the transfer window shuts at midnight on Wednesday.
He watched Monaco play Lens on Sunday evening, with a player on each side reportedly on his wanted list.
Monaco striker Manu Adebayor is available for around £6m, while Lens' attacking midfielder Olivier Thombert is another option.
Fatih Tekke at Trabzonspor remains his main target, with Latics believed to have bid 7m euros for the Turkey international.