Borussia Dortmund were held to a 1-1 home draw by Lille in their Champions League last-16 first leg on Tuesday after a second-half equaliser from visiting midfielder Hakon Haraldsson.
Last season's losing finalists were in control after Karim Adeyemi opened the scoring on 22 minutes, thumping in a low shot from the edge of the box.
But Lille striker Jonathan David took advantage of some sleepy Dortmund defending in the 68th minute, threading a ball through to Haraldsson, who was one-on-one with goalkeeper Gregor Kobel and poked home.
"The second half was not good at all. Too little intensity off the ball and too little ball possession," Dortmund captain Emre Can told Amazon Prime.
"It wasn't good enough today. But we can do better and we will."
Dortmund will need to win in northern France next week should they wish to stay in Europe and salvage what has so far been a disappointing season.
"We should have done it here in front of the fans, who were really up for it," said Adeyemi.
For Lille, the result boosts their hopes of reaching a first-ever Champions League quarter-final.
"We played a good game today, especially in the second half," said Lille coach Bruno Genesio.
"The 1-1 draw has put us in a very good position for the second leg. But we will have to deliver a very big game at home if we want to reach the quarter-finals."
- Dortmund fall back to earth -
After a surprise run to Wembley last season, Dortmund have fallen back to earth this campaign.
Sitting 10th in the Bundesliga, they needed to navigate a two-legged play-off against Sporting Lisbon to reach the Champions League last 16.
With pre-season appointment Nuri Sahin sacked as coach in January, Dortmund have improved under former Bayern Munich, Monaco and Croatia boss Niko Kovac.
In six games under Kovac, Dortmund had kept four clean sheets and won back-to-back games in the league for the first time this term.
Lille's reward for an incredible group phase, with wins over both Madrid clubs and Feyenoord and a draw with Juventus, was a trip to Dortmund.
Bidding to make the last eight for the first time in their history, Lille handed Ethan Mbappe, brother of Real Madrid superstar Kylian, his first start in the competition.
Fresh off a goal and an assist against St Pauli on Saturday, Adeyemi was again Dortmund's main man and put the hosts in front midway through the opening period.
Adeyemi skimmed a low shot into the bottom corner after Can diverted a corner in his direction.
The goal was Adeyemi's fifth in the Champions League this season, despite missing four games with a hamstring tear.
Dortmund had the ball in the net after a corner again just before half-time, but Pascal Gross was offside.
Lille found their spark as Dortmund faded in the second half.
Haraldsson showed composure to equalise with 22 minutes remaining, prodding his shot beyond Kobel as he fell to the turf, setting up a winner-takes-all second leg in Lille next week.
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