Three times European champions Inter Milan were stunned 2-0 at home by Israeli side Hapoel Beer-Sheva and Manchester United were floored by a late goal from Feyenoord as the Europa League group stage got underway on Thursday.
The Israeli champions scored twice through Miguel Vitor and Maor Buzaglo in the second half to silence a sparsely populated San Siro and inflict a painful defeat on Inter manager Frank de Boer in his first European game at the club.
Competition favourites United's trip to Rotterdam turned sour when Feyenoord's Tonny Trindade applied a slide-rule finish late in the second half to secure a 1-0 win in Group A following a poor display from Jose Mourinho's star-studded side.
Zenit St Petersburg pulled off one of the most impressive fightbacks in European competition history when they came back from 3-0 down against Maccabi Tel Aviv to win 4-3 with all the Russian side's goals coming from the 77th minute onwards.AS Roma were held to a 1-1 draw at Viktoria Plzen, while fellow Italians Sassuolo, who are making their European debut, enjoyed a superb 3-0 win over Athletic Bilbao.
Thursday's action featured the quickest goal in the competition's history when Slovan Liberec's Jan Sykora scored after 10.69 seconds in a 2-2 draw with Qarabag but late goals were the order of the day as Zenit fought back in Israel.
Zenit looked beaten when they fell 3-0 behind in the 70th minute against Maccabi but Aleksandr Kokorin headed home to begin the comeback before Eli Dasa was sent off for the Israelis in the 81st.
Further Zenit goals soon after from Brazilians Mauricio and Giuliano drew the Russians level and Luka Djordjevic remarkably grabbed the winner two minutes into stoppage time.
Roma, who have made a bright start in Serie A with seven points from their opening three games, took the lead against Plzen in Group E when Diego Perotti calmly stroked home a fourth-minute penalty after Stephan El Shaarawy was felled.
The lead lasted just seven minutes, however, as Martin Zeman's whipped cross found Marek Bakos to head the hosts level.
Italian striker Mario Balotelli was making his European debut for Nice but his new side lost 1-0 at home to Schalke 04 with Baba Rahman scoring a 75th-minute winner.
Premier League side Southampton won 3-0 against visiting Sparta Prague with a Charlie Austin double, while last season's beaten semifinalists Villarreal won 2-1 at home to Zurich with ex-AC Milan and Chelsea striker Pato among the scorers.