Elsewhere, last season’s beaten finalists Arsenal eased to victory over Lille while Barcelona came from behind to beat Galatasaray but Inter Milan lost a seven-goal thriller at home to Club Brugge.
Atletico, who lost at Liverpool in their opening European encounter, took the lead inside the opening minute in the Spanish capital through Pablo Barrios. Alejandro Grimaldo struck the woodwork from a free-kick later in the first half.
Johnny Cardoso also had a goal disallowed before the break but Ademola Lookman got Atletico’s second in the 79th minute, just after United defender Leny Yoro had been sent off.
The defeat continued the Old Trafford club’s disappointing start to the campaign and increased the pressure on manager Michael Carrick.
They have gone five matches without a victory and have won only once in seven outings, with a trip to Italy to face Como next up in the Champions League.
“Tonight is a one-off game in judgement, it is the Champions League and a tough place to come. We are doing certain things OK,” Carrick told broadcaster Amazon Prime.
Viking, who are in the Champions League after winning a first Norwegian title in 34 years, appeared to be heading for a famous win over Bayern when they led 2-0 at half-time in Stavanger.
Gianni Stensness headed them in front in the second minute and Peter Christiansen ran away to double their advantage.
Harry Kane pulled one back from a penalty early in the second half and then headed in his eighth goal of the season in nine games in all competitions.
Luis Diaz then converted as the match was turned completely on its head, but Bayern’s Michael Olise was sent off in the 74th minute – the France star was booked and then shown a second yellow seconds later for throwing the ball at his opponent.
He will therefore miss next week’s home meeting with Arsenal.
Viking snatched a memorable draw as Herman Haugen headed home in the last minute.
Speaking to Amazon Prime, Kane said Olise “will be gutted and he has to take responsibility for it. It was a mistake, and mistakes happen. He has to learn from it. It’s a shame because we have important games ahead of us.”
Arsenal were too strong for Lille as the Premier League champions won 3-0 at the Emirates Stadium with goals by Jurrien Timber, Eberechi Eze and Bukayo Saka, in the space of eight second-half minutes.
Barcelona, one of the favourites to win the competition, maintained their 100 per cent record this season with a 4-1 win over Galatasaray in Istanbul.
Russian international Aleksei Batrakov gave the Turkish champions the lead and they then had another goal disallowed, but Joao Cancelo equalised before half-time.
Lamine Yamal then turned on the style, setting up goals for Fermin Lopez and Anthony Gordon early in the second half, before substitute Karim Adeyemi sealed Barca’s victory.
Italy-born German striker Nicolo Tresoldi scored a hat-trick, including a penalty, as Club Brugge claimed a remarkable 4-3 win away to Inter at San Siro.
Romeo Vermant got the Belgians’ other goal, with Lautaro Martinez on target twice for Inter as they succumbed to a second straight European defeat.
In other games, Villarreal came from behind to beat Napoli 3-1 in Spain while RB Leipzig beat PSV Eindhoven 1-0 with a Brajan Gruda goal after Ivan Perisic failed to convert a penalty for the Dutch side.
Sporting of Portugal won 2-0 away to Lens in France with goals by Luis Suarez and Issa Doumbia, and it was a night to remember for Sabah as the rank outsiders from Azerbaijan downed Slavia Prague 2-0 in Baku.
Jamaican international Kaheem Parris and Rwanda’s Joy-Lance Mickels secured their first victory in the league phase.
Wednesday’s Champions League games include reigning champions Paris Saint-Germain at Manchester City and Real Madrid at Roma. (AFP)
