LONDON (AP) ― Barcelona and Manchester United erased early deficits to stay perfect in the Champions League group stage on Tuesday, but Chelsea got the first loss of its title defense and jeopardized its qualification hopes.

Jordi Alba’s goal four minutes into second-half stoppage time snatched a 2-1 victory for Barcelona over Celtic, keeping the competition favorites top of Group G after three games.

United’s comeback was even more impressive, recovering from two goals down to beat Braga 3-2 at Old Trafford thanks to two goals by Javier Hernandez.

Chelsea lost 2-1 at Shakhtar Donetsk to fall three points behind the Ukrainian side in Group E. Juventus couldn’t capitalize on Chelsea’s slip-up, however, surprisingly drawing 1-1 at Denmark FC Nordsjaelland.

After its stunning 3-1 win over Bayern Munich last time out, Belarus side BATE Borisov came back down to earth with a 3-0 home loss to Valencia to cede its lead of Group F to the Spanish team on goal difference.

Bayern, last season’s beaten finalist, is also on six points in a tight group after Thomas Mueller’s first-half penalty clinched a 1-0 victory at Lille.

Also, Spartak Moscow beat Benfica 2-1 to get off the mark in Barcelona’s group and move a point behind Celtic in the battle for second. Cluj conceded a late equalizer to draw 1-1 at Galatasaray but is still second behind Man United in their group.

Barcelona won its 100th Champions League match and set a new club record of 18 home matches in Europe without a loss, but the win over Celtic was much tighter than expected.

Celtic took a surprising 18th-minute lead when Javier Mascherano deflected a free kick into his own net and the Scottish side defended stoutly before Andres Iniesta tied it in the 45th.

Celtic goalkeeper Fraser Forster made a string of brilliant saves but was beaten by Alba deep into injury time, the Spain left back glancing in a cross from Adriano.

“It’s gut-wrenching,” Forster said. “Everybody’s devastated.”

United also claimed a third straight win the hard way, after Brazilian forward Alan had taken advantage of some typically shoddy defending from United this season to put Braga 2-0 ahead after 20 minutes.

Hernandez scored either side of a scrappy goal by Jonny Evans to leave United just one win away from qualification. That would make up for its surprise exit at the group stage last season.

“It’s been the story of our season at home, starting badly and losing goals. We have had to rescue games,” United manager Alex Ferguson said, after his team fell behind for the eighth time in 12 games this season.

Chelsea had been undefeated in the Champions League since losing 3-1 to Napoli in a last-16 match in March, but that record was ended thanks to goals by two of Shakhtar’s Brazilian contingent.

Alex Teixeira and Fernandinho scored either side of halftime, with Oscar’s reply from Chelsea two minutes from time proving only a consolation.

“We didn’t play well,” Chelsea defender David Luiz said. “It is a shock following some good performances in the Champions League.”

Chelsea still has two home games left, but failure to beat Shakhtar in the return match in two weeks’ time at Stamford Bridge could leave the current English leaders’ struggling to make it out of the group.

The visitors had John Terry returning at center back, wearing the captain’s armband embroidered with the slogan “Unite Against Racism” a year to the day since his infamous on-field confrontation with a Premier League opponent that resulted in him receiving a four-match domestic ban for racial abuse.

Shakhtar is three points ahead of Chelsea, with Juventus a further point adrift after needing an 81st-minute equalizer by Mirko Vucinic to avoid an embarrassing loss at FC Nordsjaelland and stay unbeaten this season.