The three-time champions had to fight hard to see off the Welsh region – they were 12 points down early on and 10 adrift shortly after half-time, but tries from Max Malins (2), Duncan Taylor and Tom Woolstencroft were enough for progression to the quarter-finals.

McCall admitted that Saracens didn’t come alive until the final quarter of the game, with late scores from Taylor and Woolstencroft a reward for how they stuck to their task.

"We had a proper test and we passed it. We didn't play as well as we'd have liked for the first 55 minutes," McCall said.

"I'm really pleased about that last 25 minutes against a good side. Everything was different - more aggressive and proactive.

"There was a different intensity about us. In the first 55 minutes we looked like a team that had a lot to lose.

"In these games against good teams like the Ospreys, everything just doesn't go your way.

"You have to dig in and go through some tough moments and tough periods. We ended up enjoying that test and relished the battle.”

Saracens’ win has set up a gargantuan quarter-final encounter with reigning champions Stade Rochelais at Stade Marcel Deflandre on Sunday, and McCall is wary of how Ronan O’Gara’s side will respond after scraping a last-gasp victory over Gloucester Rugby in the Round of 16.

"There will be another battle next weekend, which is very exciting because we've never been to La Rochelle before and they're the reigning champions,” he noted. “Gloucester might have poked the bear a little bit."

Saracens stepped up to the challenged posed by Ospreys in the Heineken Champions Cup Round of 16, director of rugby Mark McCall said after their 35-20 victory at StoneX Stadium on Sunday.