Olivier Giroud of Chelsea scores an overhead kick in the match against Atletico Madrid on Tuesday in Bucharest, Romania. Photo: VCG

Olivier Giroud's magnificent bicycle kick broke Atletico Madrid's resistance and earned Chelsea a crucial away goal on Tuesday, a 1-0 victory giving Thomas Tuchel's side a slender advantage in the Champions League last 16. 

Giroud's acrobatic strike was initially ruled out for offside but stood after VAR showed Mario Hermoso had got the final touch, delivering a huge blow to Atletico's hopes of reaching the quarterfinals. 

"I didn't know what to think about the goal, I just focused on hitting the ball," said Giroud. "I love an overhead kick and I was just pleased to see the ball hit the back of the net. I had no clue about being offside or not."

Diego Simeone's side had put on a typically disciplined defensive performance until that point but Giroud's moment of genius means they will have to score in London on March 17 if they are to avoid an early exit. 

It also continues a worrying dip for Atletico, whose lead in La Liga is also under threat after one win in four matches.

Chelsea, meanwhile, passed their biggest test since Tuchel was appointed at the end of January, backing up a strong run against lesser lights in the Premier League with a polished display against one of Europe's elite. 

"We knew their strengths and dealt with them," said Giroud. "We need to stay focused now and finish the job."

Giroud's goal in the 68th minute was only the third Atletico have conceded in 14 home legs of the Champions League knockout stages under Simeone, even if this fixture was at home only in name.

Restrictions imposed by the Spanish government meant the game had to be played in Bucharest instead of Madrid, despite the return match remaining at Stamford Bridge in three weeks' time. 

Their defeat makes it three home losses out of three for Spain's teams in the Champions League last 16 so far, after Barcelona were thrashed by Paris Saint-Germain and Sevilla were beaten by Borussia Dortmund last week.

Callum Hudson-Odoi started for Chelsea, despite Tuchel criticizing the 20-year-old's attitude against Southampton on Saturday. 

Atletico started with Suarez, Joao Felix and Angel Correa but an attacking lineup took up a typically defensive shape, a six-man wall quickly forming in front of Chelsea in the opening stages. 

The first half was tight, each side able only to create openings but failing to find the pass to make a chance. 

Edouard Mendy's heavy touch in the opening minutes almost gave the chasing Saul Niguez a tap-in while Timo Werner's angled shot was saved by Jan Oblak and Suarez miskicked at the near post. 

Chelsea looked most dangerous down the flanks, where Marcos Alonso and Hudson-Odoi pushed Atletico back. Atletico had space on the break but lacked the precision to capitalise. 

Felix sprung into life early in the second half, feeding Thomas Lemar and then meeting the Frenchman's cross with an acrobatic volley that flew over. 

The game looked destined to finish goalless only for Atletico to briefly lose shape, allowing the instinctive Giroud to take advantage. 

Alonso had raced away from Marcos Llorente down the left and his cross was diverted backward to Giroud, who brilliantly bicycle-kicked into the corner, but looked offside, only for the replay to show it was Atletico's Hermoso who had given him the assist. The goal stood and Chelsea's players celebrated, seemingly as surprised as anyone and delighted with a precious advantage.