England fly-half Owen Farrell kicked the winning penalty six minutes from time as Saracens consigned Harlequins to their first defeat in five Aviva Premiership matches this season.
Farrell scored all 18 points for the visitors, with six penalties, in a hard-fought encounter at the Twickenham Stoop.
McCall, whose side were without a win from their previous two matches, said: "It's a big relief. In the last couple of weeks we have lost ourselves a bit.
"We talked about ourselves and and what we're about as a club but we've found ourselves today."
Farrell was back to his goalkicking best after his recent sub-standard performances came under scrutiny, but McCall insisted he never had any worries about his young marksman.
He told the post-match press conference: "Owen came into this match under a little bit of pressure from you guys but he's an international player so there were no worries there."
McCall expressed concern that referee Andrew Small did not refer the only try of the match, scored by Quins scrum-half Danny Care, to the television match official.
He said: "I didn't get a great view but it looked like there had been a knock-on. He does have the facility to go upstairs but he didn't."
Farrell, whose goalkicking practice had been restricted by a recent groin injury, said: "I'm not concerned about it at all. I hadn't practised anywhere near as much as I wanted to.
"That isn't an excuse but I stuck to what I knew and going into this one I'd been kicking well in training.
"We've a brilliant kicking coach in Dan Vickers and we've made little changes but I'm still kicking basically the same."
Farrell added: "We were back to where we play as a team, with the intensity we showed. We put things right today.
"The main thing for us was to get back playing for each other. It never really went away - we just needed a little reminder."
Harlequins director of rugby Conor O'Shea refused to blame misfiring goalkicker Nick Evans for his side's defeat.
The former New Zealand fly-half missed four penalties, including three fairly straightforward second-half shots, any one of which could have extended Quins' 100 per cent start to the season.
After the game Evans tweeted: "Tough day at the office, apologise for the kicking, you have days like that, but she is a long season and again thanks for your support."
But O'Shea said: "Of course it would have been completely different but he's won a million games for us and hopefully he'll win a lot more. He's an outstanding player."
The Quins boss added: "We gave them six penalties and they kicked six penalties. We weren't up to the levels we want to be.
"It became the game they wanted in terms of flow but that's a credit to them.
"We're disappointed to lose but it's a long, long season.
"We should have won that game but we didn't. We didn't take our opportunities.
"It wasn't a good game of rugby at all but it was tight.
"The big games are decided by very small margins and they didn't go our way this time.
"We never get carried away when we win, we're not going to get carried away when we lose."
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