Hulk put the visitors in front after just five minutes with an assured finish after collecting Oleg Shatov's measured through-ball.
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Nicolas Gaitan tried to claw the home side back into the game within five minutes but his strong strike was dealt with by Juri Lodygin.
Hulk flashed the resulting free kick wide, but Witsel made it 2-0 shortly after with a strong header that just about crept over the line.
Hulk continued to cause havoc for the home side and went close to grabbing his second of the night in the 31st minute when he drilled a low shot inches wide of the near post.