Maurizio Sarri's Chelsea maintained their flying start to the season with a 1-0 victory at PAOK Salonika in their opening Europa League Group L fixture on Thursday.
Brazil midfielder Willian's early strike proved sufficient to seal the points, although Chelsea could have won by a wider margin had they been sharper in front of goal.
The Premier League leaders have now won their opening six games under Sarri, who replaced Antonio Conte in July.
Meanwhile, Unai Emery returned to the competition with his Arsenal side beating Ukrainians Vorskla Poltava 4-2 as Pierre-Emerick Aubameyang netted twice.
Emery's 32nd Europa League win was a record for a manager.
German club Eintracht Frankfurt returned from the south of France with a surprise 2-1 victory over Marseille.
Last season's runners-up made the perfect start with Lucas Ocampos scoring in the third minute but Eintracht hit back through Lucas Torro before Luka Jovic grabbed a late winner.
Eintracht, playing in their first European campaign since the 2013-14 season after winning the German Cup, were joined at the top of the early Group H standings by Lazio who beat Apollon Limassol 2-1 with goals by Luis Alberto and Ciro Immobile.
Sevilla, Europa League winners in 2014, 2015 and 2016, also opened with a victory, thrashing Standard Liege 5-1 in Group J with Ever Banega and Wissam Ben Yedder both scoring twice.
The so-called "energy drink derby" turned into a thriller with last season's semifinalists Red Bull Salzburg winning 3-2 at RB Leipzig in the first competitive meeting of the teams.
The hosts, whose full name is RasenBallsport Leipzig, battled back from 2-0 down to level the scores but Fredrik Gulbrandsen struck for the visitors in the final minute.
The energy drinks manufacturer last year argued it no longer has a controlling stake in the Austrian club and merely sponsors it, satisfying UEFA that the two clubs could face each other.
Also in Group B, Celtic beat Rosenborg 1-0 thanks to a late goal by substitute Leigh Griffiths.
Celtic's Glasgow rivals Rangers, managed by Champions League and UEFA Cup winner Steven Gerrard as a player at Liverpool, twice battled back to draw 2-2 at Villarreal in Group G.
Kyle Lafferty's late goal earned the Scottish club a point.
Dudelange, the first team from Luxembourg to reach the Europa League group phase, welcomed seven-time European champions AC Milan to the Stade Josy Barthel.
Despite the gulf in status, Dudelange produced a resolute display and Milan needed Gonzalo Higuain's deflected 59th minute effort to seal a 1-0 victory in Group F.
The other match in the group ended scoreless between Olympiakos and Real Betis.
In Group D, Croatians Dinamo Zagreb enjoyed a 4-1 victory over Fenerbahce but there was a surprise as Anderlecht went down 1-0 to Spartak Trnava in Slovakia.
In other matches, Rapid Vienna beat Spartak Moscow 2-0 in Group G.
In Group I, Genk defeated Malmo 2-0 and Besiktas eased past newcomer Sarpsborg 3-1.
In Group A, Bayer Leverkusen rallied from two goals down to win 3-2 at Ludogorets Razgrad in Bulgaria.
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