A goal deep in injury time by Ghanaian star Andre Ayew gave Marseille a 1-0 win over 2010 champions Inter Milan in their UEFA Champions League last 16 first leg and cast further doubt over Claudio Ranieri's future on Wednesday.
There was also a late goal in the night's other tie as substitute Valentin Stocker's 86th minute effort gave unheralded Swiss side Basel a shock 1-0 home win over German giants Bayern Munich.
It continued a worrying slump in Bayern's fortunes which has seen the four-time European champions win just three of their last seven games.
Basel's win saw them become only the fifth team in the competition's history to beat both the German side and Manchester United in the same campaign - four of them went on to win the trophy.
Basel had the better of the opening 20 minutes after Bayern's French star Franck Ribery had given them a wake-up call when he broke the offside trap but his shot was turned round the post by the Swiss side's goalkeeper Yann Sommer.
Basel, though, stormed back after that let-off and twice went agonisingly close to breaking the deadlock in a matter of minutes. First Aleksandar Dragovic's header looked to be heading for the back of the net only for German number one Manuel Neuer to pull off a miraculous stop which still saw the ball bounce along the line before it was hacked clear.
It was the turn of veteran former Swiss international striker Alexander Frei to be left frustrated a minute later as he turned smartly inside the box but while his shot beat Neuer it cannoned off the bar.
Sommer pulled off a great save midway through the second-half as he tipped over the bar a fierce long range effort by Bayern's experienced German fullback Phillipp Lahm.
However, the deadlock was broken as the match entered its closing stages after Jacques Zoua threaded a superb ball to the unmarked Stocker inside the box and he made no mistake sliding the ball between Neuer's legs.
"It was a very difficult game, Bayern made us run a lot," admitted Sommer. "We have beaten two of the best teams in the world here now - Manchester United, from who we took four points in total, and Bayern which is unbelievable for a Swiss team.
"But we are a good side and we believe in ourselves so I don't think Bayern under-estimated us."
His Bayern counterpart Neuer conceded that they had not deserved much from the match and their problems needed fixing quickly. "It's of course a very bitter defeat for us," he said.
"You can't even say it wasn't deserved, we didn't play well and didn't take our chances. We have to deal with this internally now and fix the problems quickly. There were too many mistakes and we have to cut them out."
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Marseille and Inter failed to deliver much in the sense of entertainment until Ayew's goal in the third minute of injury time gave the 1993 champions some breathing space when they travel to Milan.
"We showed desire and determination," said Marseille coach Didier Deschamps, who captained the 1993 side. "It was good for us to score at the end, because it could have been a draw.
"If we don't concede in the return leg, we'll go through, but that won't be enough. We'll try to score a goal, but in any case it will be a complicated match."
Ranieri remained defiant both about his own position as well as his side reaching the last eight. "We played a good match, in which we created more chances than them, and we didn't deserve to leave beaten," he said.
"It's a shame to concede a goal from one of their only chances, but the match isn't over. There are still 90 minutes to go and, with a full stadium, a turnaround is possible."