American Jesse Marsch lost his first Bundesliga game as head coach of RB Leipzig on Sunday after his side suffered a surprise 1-0 defeat at Mainz, whose preparations had been badly hit by an outbreak of Covid-19.
After winning back-to-back Austrian league and cup titles with RB Salzburg, Marsch moved to their sister club this season to replace Julian Nagelsmann, who is now at Bayern Munich.
There was a minute's silence before kick-off to pay respect to German legend Gerd Mueller who died in the early hours of Sunday.
The hosts deservedly took an early lead when captain Moussa Niakhate hooked the ball into Leipzig's goal on 13 minutes.
It was a remarkable display from Mainz whose preparations were disrupted by having 11 players quarantined as striker Karim Onisiwo was one of three squad members to test positive for coronavirus.
Head coach Bo Svensson had to reshuffle his starting team, but his side turned in a determined display in sweltering temperatures.
"We didn't have a good start and the early goal hurt us, it was a perfect situation for Mainz who could defend deeper and deeper," Marsch told broadcaster DAZN.
"They defended well - you have to say - and we didn't find enough room with the ball. We didn't have enough tempo and didn't create enough."
Much is expected of last season's runners-up Leipzig, who host champions Bayern in the Bundesliga on September 11.
"We had a good pre-season and this game didn't go in the direction we wanted, but for me, nothing has changed. This is a good reminder that we have more work to do," insisted Marsch.
- 'It wasn't good enough' -
It turned into a frustrating afternoon for Leipzig's attack led by Sweden playmaker Emil Forsberg.
"That was too little from us," said Forsberg.
"We didn't press them enough. We didn't find enough solutions to break down their defence. It wasn't good enough today.
"We have to do better against Stuttgart (at home) on Friday."
Leipzig's new striker Andre Silva, signed for a reported 23 million euros ($27 million) from Eintracht Frankfurt, was repeatedly denied by Mainz goalkeeper Robin Zentner.
Mainz thought they had doubled their lead late on when defender Alexander Hack smashed home a shot from a corner, but replays showed the ball had previously gone dead behind the Leipzig goal.
At the other end, Leipzig defender Nordi Mukiele had a shot blocked by Hack.
Later on Sunday, Cologne fought back to seal a 3-1 victory at home to Hertha Berlin.
Hertha's new-signing Stevan Jovetic got off to a dream start in the Bundesliga when the former Monaco striker tapped home with just six minutes played.
Cologne fought back when veteran French striker Anthony Modeste, 33, headed them level on 41 minutes.
Home midfielder Florian Kainz then turned the game when he scored with a second-half header and left-footed shot to give Cologne's new head coach Steffen Baumgart a winning start.
On Friday, champions Bayern were held to a 1-1 draw at Borussia Moenchengladbach.
Borussia Dortmund striker Erling Braut Haaland then played a part in all the hosts' goals in a 5-2 thrashing of Frankfurt on Saturday.
