BUCHAREST, Romania — After his great overhead kick found the net to break the deadlock in a difficult match, all Olivier Giroud could do was wait.

And wait and wait.

Giroud’s 68th-minute bicycle-kick goal against Atlético Madrid was initially disallowed for offside and it took nearly three minutes for video review to reverse the call and secure Chelsea the 1-0 away win in the first leg of the round of 16 of the Champions League on Tuesday.

Giroud was clearly in front of the defenders when he pulled off his acrobatic shot and few Chelsea players complained when the linesman raised his flag, but VAR determined that the ball came from Atlético defender Mario Hermoso instead of Chelsea midfielder Mason Mount, thus annulling the offside.

“I did not know what to think about the goal, I just focused on hitting the overhead kick and was pleased to see it go in the back of the net, I had no clue about being offside," Giroud said. “Mason Mount said he did not touch the ball. Good for the team, good for me.”

The result kept Chelsea coach Thomas Tuchel unbeaten in eight matches since he took over the squad to replace Frank Lampard.

“Fantastic result, fantastic goal. Well deserved,” Tuchel said. “It was a very disciplined performance — a deserved shutout."

Atlético was the home team but the match was played in Bucharest, Romania, because of travel restrictions preventing visitors from Britain entering Spain.

The second leg will be on March 17 in London.

In the other round-of-16 match on Tuesday, Bayern Munich defeated Lazio 4-1 in Italy.

It was the second consecutive loss for Atlético after a seven-match unbeaten streak in all competitions. It was also the eighth straight game in which the Spanish club has conceded a goal, extending its worst run without a clean sheet since coach Diego Simeone arrived in late 2011.

“It’s been a difficult week but we have to keep competing,” Atlético midfielder Koke Resurrección said. “We have to raise our heads and try to win the second leg. There’s no other option for us.”

It had been a lacklustre match until Giroud’s goal, with neither team managing to create many significant scoring opportunities and with the goalkeepers not having to work too hard. Chelsea controlled possession and looked a bit more dangerous, but both sides appeared to be satisfied with the scoreless draw and didn’t take too many risks.

“We knew they were ready to suffer with eight people in the box,” Tuchel said. “The intention was to keep the intensity high. This is what we did very good. We never let them breathe or come out for counter-attacks. We have a big reward with this result. This is one of the toughest challenges to open a defence like (Atlético's).”

Atlético was outshot by Chelsea and finished the match with no attempts on target.

“We know the importance of the away goal in Europe so that is why I was pleased to help the team win the game,” Giroud said. “We managed it well and we were confident but faced a great team and I think we were very committed and knew their main strengths. We dealt with it, but we have to stay focused and complete the job.”

Hermoso was trying to clear the ball from the area while under pressure from Mount and kicked it backward. Giroud reached up high with his left foot to send the ball toward the corner past Atlético goalkeeper Jan Oblak.

“The game was decide on details,” Koke said. “It didn't look like a dangerous play but they ended scoring a great goal.”

Mount and Jorginho were shown yellow cards and will miss the second leg because of accumulation of cards.

Simeone had to improvise with midfielder Marcos Llorente as a right back against Chelsea because of several absences on defence, including Kieran Trippier following an English betting investigation.

The teams had played in the group stage of the Champions League in the 2017-18 season, with Chelsea winning 2-1 in Spain before a 1-1 draw in London. Atlético eliminated Chelsea in the semifinals in 2014.

It was in Bucharest that Simeone won his first title with Atlético, the 2012 Europa League.

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