Cristiano Ronaldo scored two, including a stoppage-time equaliser, as Manchester United came from behind twice to earn a 2-2 draw away to Atalanta in the Champions League on Tuesday.

The 36-year-old Ronaldo has now scored five goals in four games for United in this Champions League campaign and has nine in 11 outings for the club this season.

His outstanding finishing secured a vital point for United, who was minutes away from slipping to third in the group but instead finds itself top on seven points.

Atalanta took a 12th-minute lead when burly striker Duvan Zapata, a thorn in United's side all through the match, cut in from the left and fed Josip Ilicic and the Slovenian's low drive crept under the body of United keeper David De Gea.

Ole Gunnar Solskjaer's side had found a system and style that looked effective in its 3-0 win at Tottenham Hotspur in the Premier League on Saturday but its adoption of three central defenders had to be abandoned in the 38th minute when French centre back Raphael Varane suffered an injury and had to be replaced.

READ: Bayern beats Benfica to qualify for Champions League last 16

With Eric Bailly starting for the injured Victor Lindelof, United had no choice but to revert to an orthodox four-man defence and it once again struggled in that formation.

But just before the break, United produced a superbly worked goal with a flowing passing move ending with a clever back-heel from Bruno Fernandes to Ronaldo, who buried the chance.

Gian Piero Gasperini's Atalanta was well on top after the break and it restored its advantage in the 56th minute when Zapata broke past Harry Maguire, burst into the box and beat De Gea. The linesman's flag was raised for offside but after a lengthy VAR review the decision was over-turned and the Italian side had the lead.

United desperately searched for an equaliser but it was ragged and lacked any sort of fluency in midfield or attack or solidity at the back.

But right at the death, Ronaldo pounced on a loose ball on the edge of the box and with his trademark technique and precision blasted home a low volley to earn a precious point.

"We never give up, we believe until the end, it is a good result for us," said Ronaldo.

"The beginning was tough, we knew Atalanta would do a lot of pressure, they have a fantastic coach, when I played at Juventus they were always difficult to play against. We were a little bit lucky in the end but that is football," he added.

"We have to still improve, we have different players, different system, we have to adapt with each other, but it will take time. We have time to improve and be better."

Ronaldo's performance left Gasperini laughing wryly at the notion that the 36-year-old is to be blamed for United's inconsistent form.

"Some even managed to say he was a problem, imagine Ronaldo as a problem! He never gets it off target - half the time he scores, half the time it is saved," Gasperini said.

At 36, Ronaldo's lack of pressing work had led some critics to recently question if he was unbalancing the United side, but Solskjaer clearly understands the quality he brings to the side.

READ: There is interest from Newcastle but no offer, says Emery

"Cristiano is just incredible if there is anyone you want a chance to fall to ... and it’s a difficult chance. He keeps his eye on the ball and his technique on that volley is incredible," said the Norwegian.

“In the Champions League, great players can change a game that you deserved to win and then don’t. A third goal would’ve killed it, that was the case in Manchester too, and we certainly had the chances to go 3-1 up in both games," he said.

Solskjaer felt the performance had also answered another criticism of his players heard in the aftermath of the recent 5-0 home loss to Liverpool.

"Definitely no-one can question the character of these players. They just don’t give up, they don’t give in and they keep going. We had to make a few changes and they worked," he said.

In the other Group F match, Villareal beat Young Boys 2-0.

United and Villarreal are level on seven points with Atalanta on five and Switzerland's Young Boys on three.