Feyenoord's goal in a rain-soaked 1-0 win over Milan in Rotterdam on Wednesday night came in the third minute and relied on France goalkeeper Mike Maignan spilling Igor Paixao's shot into the net.
"We can turn it around in the second leg," former Manchester City and now Milan defender Kyle Walker told Sky Sport.
"We have to learn from tonight. It's not just the forwards - all the team needs to contribute to score goals."
It was a quick winning start for the Dutch side's interim coach Pascal Bosschaart, in his first game after the firing of Brian Priske two days earlier.
Sandwiched between stints in the Netherlands' Eredivisie with FC Utrecht and ADO Den Haag, Bosschaart was a defender for Feyenoord from 2004-06.
The now 44-year-old also played in the A-League Men for two seasons with Sydney FC between 2011-13.Â
Bayern, the German Bundesliga leaders, got high-class strikes from Michael Olise and Harry Kane either side of halftime in a 2-1 win at Celtic Park.
"One of the world's best strikers shouldn't be left free in the box," a disappointed Celtic boss Brendan Rodgers said of the poor defending of England skipper Kane for Bayern's second.
The visitors had joined Real Madrid and Manchester City as Champions League title winners in the past five years who surprisingly found themselves in the playoffs because they finished outside the top eight in the new 36-team single standings format. Madrid won 3-2 in Manchester on Tuesday.
Elsewhere, Benfica won 1-0 at Monaco with another goal from Vangelis Pavlidis, a delicate chip in the 48th. The in-form Greece forward's sixth goal in the competition followed a hat-trick against Barcelona last month.
Club Brugge scored with a disputed penalty kick in added time to beat Atalanta 2-1 in a meeting of teams that finished 24th and ninth, respectively, in the 36-team standings two weeks ago.
The top eight teams had advanced direct to the round of 16 in March.
Swedish international Gustaf Nilsson slotted home the spot kick after Brugge had led on former Barcelona forward Ferran Jutgla's shot in the 15th minute and Atalanta levelled in the 41st on Mario Pasalic's header.
With AAP.
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