A Hakan Calhanoglu penalty gave Inter Milan a 1-0 victory over Arsenal in the Champions League on Wednesday, while a 93rd-minute winner ensured Atletico Madrid left Paris with all three points.

The Italian champions remain undefeated in the competition this season and sit fifth on 10 points at the midway point of the new league phase format.

"I think we played a great game against a strong side who play with great intensity," said Inter coach Simone Inzaghi.

Arsenal, on the other hand, experienced defeat for the first time in Europe this season and lie three points and seven places behind their opponents.

The match at the San Siro looked set to go into the break goalless until a penalty was signalled against Mikel Merino after Mehdi Taremi's flick deviated the ball into the Arsenal player's raised hand from close range.

"We were very harshly done by," Arsenal boss Mikel Arteta told TNT Sports. "There is no deflection, nothing you can do in the box, so can he get away from it?"

Calhanoglu stroked home the resulting spot-kick three minutes into first-half injury time.

Yann Sommer and Denzel Dumfries combined on the line to deny Gabriel Magalhaes a leveller shortly before the hour.

Arsenal cranked up the pressure in the second half but were unable to break down Inter's solid defensive block as the Premier League side fell to a second defeat in four days.

Barcelona beat Red Star Belgrade 5-2 in Serbia to claim sixth spot in the standings.

The Catalans took the lead on 13 minutes via a stooping header by defender Inigo Martinez.

But Red Star struck back just prior to the half-hour when Silas Mvumpa sprang the Barca offside trap and lifted the ball past Inaki Pena.

Robert Lewandowski effectively ensured Barca stayed in the automatic qualification spots with a quick-fire double either side of the break.

Raphinha and Fermin Lopez then netted, before Felicio Milson curled in a late consolation for the hosts.

- PSG in trouble -

Atletico stunned PSG 2-1 in the French capital as Angel Correa's stoppage-time winner gave the Spaniards a second Champions League win this term.

"Paris played very well, they attacked the whole match, but we were confident, we worked hard in defence and as a team, and we got our goal at the end to claim victory," Correa said to Movistar.

The loss means the French champions sit in the elimination zone with one win and a draw from four, with matches against Manchester City and Bayern Munich to come.

Warren Zaire-Emery sent PSG ahead with a dinked finish past Jan Oblak on 14 minutes, before Nahuel Molina drilled in an equaliser four minutes later.

The home team pressed as the match wore on but left themselves exposed as Oblak's throw found Antoine Griezmann on the break and the Frenchman's pinpoint pass landed at the feet of Correa, who cut in and finished past Gianluigi Donnarumma.

Jamal Musiala struck in the 67th minute to get Bayern Munich's stuttering campaign back on course with a 1-0 win at home to Benfica.

The six-time winners' record of two wins and two defeats leaves them mid-table with four matches remaining.

Aston Villa's 100 percent record in the Champions League ended with a 1-0 defeat at Club Brugge, sparked by a bizarre penalty conceded by Tyrone Mings.

After making his debut in the competition in just his second match back after a long injury lay-off, the England centre-half gifted Brugge a penalty in the 51st minute after he picked up a short goal kick taken by Emiliano Martinez.

Hans Vanaken stroked home from 12 yards to drop Villa to eighth.

Brest continued their excellent start to life at European football's top table, a 2-1 win at Sparta Prague taking them to fourth place.

Second-half strikes by Ademola Lookman and Nicolo Zaniolo gave Europa League champions Atalanta a 2-0 win at Stuttgart.

RB Leipzig picked up their first points of the campaign with a 3-1 victory in the Netherlands against 10-man Feyenoord.

Shakhtar Donetsk of Ukraine defeated Young Boys 2-1, condemning the Swiss side to a fourth consecutive defeat in the competition.