Saracens boss Mark McCall says his side need to raise their game and be more positive in future knockout ties after they survived a scare in their European quarter-final.

The Premiership leaders had home advantage on Saturday but were trailing against an injury-hit Northampton Saints team with just 11 minutes left – and it took late tries from Chris Ashton and Chris Wyles to secure a 29-20 victory, setting up a semi-final against Wasps.

“We were nowhere near our best and the last few weeks in the Premiership were almost too easy for us in a way,” said director of rugby McCall. “These games are different, there’s a lot at stake.

“This was the first game of the season where it’s on the line and if you lose you’re out of the competition. Maybe we played not to lose a bit and we were lucky to be only four points down at half-time. We know we’ll have to improve a lot of things against Wasps in the semi-finals.”

Ashton, whose crucial try was his third in two games since his return from a 10-week ban, said: “We were off the pace and at this level it makes such a big difference. We always knew we had it in us to come back.

“We felt like we had everything to lose, but we’re a good team and just need to keep confident with it at times.”

Saracens were big favourites to win Saturday’s clash, having won all six of their pool matches in the Champions Cup, while their side included six members of England’s Grand Slam-winning Six Nations squad.

Meanwhile, the visitors were missing the likes of Dylan Hartley, Tom Wood and George North due to injury – but the Saints led 10-6 at the break after a converted try from Ken Pisi and a penalty from Stephen Myler.

Owen Farrell – who scored with all of his seven kicks at goal to contribute 19 points – exchanged penalties with Myler after the break, but Saracens were 13-12 behind as the final 10 minutes approached.

That was the cue for Ashton’s heroics, and Farrell slotted over the conversion before kicking another penalty to put the hosts 22-13 up.

Wyles then added another converted try three minutes from time and, although Courtney Lawes went over the whitewash at the other end just before the final whistle, Saracens were able to breathe a sign of relief as they progressed into the final four.

They will be the hosts for another all-English tie against Wasps on Saturday April 23 and will aim to avenge the heavy defeat they suffered in the league earlier this year.

Wasps won 64-23 in February, with Sarries conceding the most points at home in their history.