Argentina's World Cup winner Exequiel Palacios struck twice from the spot as Bayer Leverkusen blew the Bundesliga title race wide open with a shock 2-1 win over Bayern Munich on Sunday.

With a little help from VAR, Leverkusen came from behind to hand coach Xabi Alonso a famous win on his first reunion with former club Bayern and keep the champions from regaining top spot.

"It's an unbelievable feeling. I'm so proud of the way we played today," said Alonso, who played for Bayern from 2014 to 2017.

Bayern are a point behind leaders Borussia Dortmund and the two sides set to meet in the next round of games on April 1.

"That is now a must-win game for us, because it will be very difficult to win the title otherwise," said Bayern coach Julian Nagelsmann.

"It was a deserved defeat today. Apart from the last 10 minutes, they were the better team," he added.

Bayern sporting director Hasan Salihamidzic was scathing in his criticism of the performance.

"We let ourselves be overrun by a team who played in midweek. That's not what it means to be Bayern Munich," he said.

Bayern survived an early chance from Jeremie Frimpong before taking the lead themselves when Odilon Kossounou deflected a Joshua Kimmich shot into his own net.

The hosts continued to cause Bayern problems, however, and fully deserved their equaliser from the penalty spot on 55 minutes.

Amine Adli was initially booked for diving after he was clipped by Benjamin Pavard, but the decision was reversed by VAR and Palacios converted from the spot.

The scene repeated itself 20 minutes later as Adli was brought down by Dayot Upamecano just inside the penalty area.

Once again, he was booked for diving, and once again, Palacios smashed the ball into the bottom corner after the intervention of VAR.

"VAR was a lifesaver today and it was a perfect example of how the system should work," said referee Tobias Stieler.

The win also kept Leverkusen afloat in the race for Europe, with Alonso's side now just three points adrift of sixth.

Elsewhere, Union Berlin gave their Champions League hopes a boost as a rare goal from Rani Khedira helped them to a 2-0 win over Bundesliga top-six rivals Eintracht Frankfurt.

Khedira - the brother of 2014 World Cup winner Sami - stabbed in the opener to score only his seventh goal in 194 Bundesliga appearances and lift Union back into third place.

"It's also my first goal for Union so I am very happy," Khedira told Dazn. "Today was much more about mentality than about tactics."

Both sides came into the game on five-game winless runs and trying to bounce back after being dumped out of European competition in midweek.

Frankfurt had the lion's share of the chances in the first half, with both Randal Kolo Muani and Daichi Kamada coming close.

Yet the hosts took the lead just after the break when Khedira prodded the ball home from close range after Frankfurt failed to clear a corner.

Sheraldo Becker nutmegged Frankfurt keeper Kevin Trapp to find the net again for Union on 69 minutes, but the strike was ruled out for offside.

Trapp was left blushing when he again let the ball through his legs a few minutes later to allow Kevin Behrens to double the lead.

Union -- unbeaten in 18 home games in the league -- are now two points ahead of Freiburg, who climbed to fourth with a 1-1 draw away to Mainz.

Freiburg looked set for victory after a mistake from Mainz keeper Robin Zentner allowed Japan international Ritsu Doan to steal in and score his second goal in two games.

Yet a late, smash and grab equaliser from Karim Onisiwo snatched two points away from them in injury time.