"In the end, the mentality, the quality that we have shows one more time that we believe until the end and we are happy that we take the three points back home," he added.

Alonso also put the team's habit for late goals down to their mindset.

"It's difficult to explain why we always score late goals," he told a news conference. "We can't train that and I can't influence it. It's the mentality of the team."

Xhaka had given the visitors the lead with a thunderous 25-yard strike in the 12th minute and Wirtz made it 2-0 in the 38th after Gladbach failed to clear their lines.

Leverkusen then hit the woodwork twice, while Gladbach had a goal chalked off after a video review just before half-time.

But Nico Elvedi started the hosts' comeback after 59 minutes and new signing Tim Kleindienst leveled it up in the 85th.

As so often with Leverkusen, there was still time for a final twist.

The visitors were awarded a penalty for a foul in the area deep into stoppage time, and while goalkeeper Jonas Omlin saved Wirtz's spot kick he couldn't prevent last season's Bundesliga player of the year from slotting in the rebound as Leverkusen took their unbeaten run in the league to 35 games.

"We had the feeling at 2-2 we are still in the game," Xhaka said. "Monchengladbach were putting some defensive players on so they give us more time in the midfield and after we have the players who have the quality to score, to finish the action, and we did it."

Alonso, though, saw room for improvement as Leverkusen look to defend their title this season.

"It was an intense first Bundesliga game for us," he added. "A lot of things happened in the second half, it was full of emotion right to the end. We did well in many phases.

"But we weren't always so compact today, we were also a bit passive in some phases. We have to do that better. We have to be more aggressive."

Play had been briefly halted at the start of the second half after fans lit multiple flares in the stands and part of the field was covered in smoke.