Unai Emery's side were heading for a demoralising defeat, three days after losing meekly to Sheffield United in the Premier League, but substitute Pepe's late intervention kept the Gunners top of Group F with a maximum nine points.
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Arsenal's young guns continued to shine as they dismantled Standard Liege 4-0 on a hectic night of Europa League action that produced a full house of Spanish victories on Thursday. A summary of the matches.
Juve forward Cristiano Ronaldo had an unusually quiet game after scoring a hat-trick against Atletico in last year's competition, although he came within inches of grabbing a last-gasp winner when he sent a shot just past the far post.
Here are the images that encapsulated the biggest moments in the month of August.
Manchester United, winners of the competition in 2017, will have a lot of travelling to do to Eastern Europe after being drawn alongside Kazakhstan side Astana, Serbia's Partizan Belgrade and Dutch side AZ Alkmaar.
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Ajax, semi-finalists last season, came from behind to beat PAOK 3-2 for a 5-4 aggregate win over the Greeks while Red Star knocked out FC Copenhagen on penalties after a bizarre shootout involving 22 spot-kicks.
Porto goalkeeper Iker Casillas, who suffered a heart attack in May, has been registered by the club to play in this season's Portuguese league.
Azeri champions Qarabag took a big step towards the playoff round with a 2-1 win at Cypriot side APOEL but Dinamo Zagreb left their progress hanging in the balance after the Croats played out a 1-1 home draw against Hungary's Ferencvaros.
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Manchester United manager Ole Gunnar Solskjaer is eager to build his team around midfielder Paul Pogba despite media speculation linking the French World Cup winner with a move away from Old Trafford.
Argentina can look forward to a mouthwatering Copa America semi-final clash with Brazil after delivering a much-improved display to beat Venezuela 2-0 in the quarter-finals in their first game at the Maracana since losing the 2014 World Cup final.
Gabriel got the winning kick for Brazil after Gustavo Gomez and Derlis Gonzalez missed for the visitors. Roberto Firmino pulled his spot kick wide for the hosts.
A late header from Edinson Cavani gave Uruguay a 1-0 win over Copa America holders Chile which saw them snatch top spot in Group C at their opponents' expense and set up a quarter-final meeting with Peru.
But despite some early close attempts from Uruguay, Japan began to impose themselves on the game and Koji Miyoshi gave them the lead in the 25th minute with a confident finish following a counterattack.
Uruguay crushed Ecuador 4-0 in their Copa America opener on Sunday with help from an early sending off that deflated their opponents and assured the 15-times champions the simplest of starts to their campaign.
Philippe Coutinho scored a second half double and Everton added a cracking third as Brazil recovered from a sleepy start to beat Bolivia 3-0 in their Copa America opener on Friday.
Guedes, 22, nutmegged Matthijs de Ligt, exchanged passes with Bernando Silva and then beat goalkeeper Jasper Cillessen with a shot from the edge of the area on the hour for his fourth international goal in 17 appearances.
Netherlands capitalised on two England defensive mix-ups in extra time as they came from behind to win their Nations League semi-final 3-1.
Evergreen Cristiano Ronaldo scored a hat-trick, including two late goals, to give Portugal a 3-1 win over Switzerland in a Nations League semi-final featuring an extraordinary VAR incident on Wednesday.
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The wife of Spain's World Cup-winning captain Iker Casillas, Sara Carbonero, has announced that she has undergone surgery for cancer just three weeks after the goalkeeper suffered a heart attack.
Hegerberg hat-trick fires Lyon to fourth straight Champions League
Casillas, 37, would not confirm the decision, saying in a tweet that "a day will come when I will have to retire. Leave me to announce that news when the time comes."
'This is about him. This is a reflection of his personality -- don't give up -- his fighting spirit, every player giving everything'
Porto goalkeeper Iker Casillas was released from hospital on Monday after suffering a heart attack in training last week.
'They were better than us for some spells and we know what awaits us over there' Valverde pointed to his team's sensational exit from last year's competition to AS Roma after a 4-1 cushion from the first leg and said they would be taking nothing for granted in Tuesday's return game at Anfield.
Spain's World Cup winning captain Iker Casillas, 37, suffered a heart attack while training with his team Porto on Wednesday and was taken to hospital.
Liverpool beat Porto 4-1 at the Dragao Stadium on Wednesday to advance 6-1 on aggregate with their attacking trio of Mohamed Salah, Sadio Mane and Roberto Firmino all on target once again.
Tottenham Hotspur reached the semi-finals of the Champions League on away goals after a 4-3 (aggregate 4-4) defeat to Manchester City in a breathtaking quarter-final second leg game on Wednesday.
'Porto are a really, really good football team. We have to play at our limit 100 percent'
IMAGES from the UEFA Champions League quarter-final 2nd leg matches played on Tuesday
An Aaron Ramsey strike and a Kalidou Koulibaly own goal gave Arsenal a 2-0 victory over Napoli in the first leg of their Europa League quarter-final, while Chelsea beat a stubborn Slavia Prague 1-0.
Rewind five years and Liverpool hosted Chelsea with three games remaining, knowing victory would have left them six points clear and a first league title since 1990 almost secure.
Images from the UEFA Champions League matches played on Tuesday
Mbappe struck in the 74th minute to put PSG on 80 points from 29 games and on the brink of retaining the title with second-placed Lille, who beat Nantes 3-2 away earlier on Sunday, still 20 points behind having played a game more.
Liverpool face Spurs in the game of the weekend, a day after title rivals Manchester City travel to struggling Fulham.
Christian Pulisic scored his 10th goal for the United States before being substituted after picking up a knock in a 1-1 draw with Chile in a friendly in Houston on Tuesday.
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