Martin Ellingsen's long-range strike gave the Norwegian champions a shock lead at Emirates Stadium on Friday (AEDT), but Kristoffer Haugen turned into his own net just before the break.

Substitute Sheriff Sinyan also scored at the wrong end before Pepe drilled home, and Willock added a fourth late on as a much-changed Arsenal raised their game in the second half.

A third win out of three puts Mikel Arteta's six three points clear of their opponents at the top of Group B and well on course to qualify for the knockout stages.

Martin Bjornbak was on hand to clear after Eddie Nketiah dinked an effort beyond Molde goalkeeper Andreas Linde early on, but Arsenal were lacklustre and they fell behind 22 minutes in.

Bernd Leno's casual kick was nodded to Magnus Wolff Eikrem, who picked out Ellingsen with an incisive first-time pass and the unmarked midfielder bent a clinical left-footed strike into the far corner from 25 yards.

Arsenal finally raised the tempo and Nketiah had a goal ruled out when it appeared to be Willock who was marginally offside, but the pair combined at the end of a brilliant rapid counter-attack just before half-time that resulted in Haugen putting the ball through his own net at full stretch.

Sead Kolasinac missed an open goal from close range early in the second half when Linde palmed a cross into his path, but two goals in the space of seven minutes put Arsenal in command.

Sinyan put through his own goal after the lively Willock played a one-two and knocked the ball across the six-yard box, before Pepe fired in first time from just inside the penalty area when Bukayo Saka picked him out.

Pepe then turned provider for Willock, who lashed home a deserved fourth clinically in the closing stage.