With nine minutes left on the clock, the forward tucked the ball into the back of the net to secure a 3-2 win against The Hammers on aggregate.
West Ham much improved as they suffer narrow defeat in Betway Cup
Right from the word go West Ham came out the blocks, delivering a much improved display despite the overall result. Naturally, that is of little surprise given the team included a number of high-profile, experienced players. Pablo Zabaleta and Joe Hart were among eight senior internationals to feature, alongside Jose Fonte, Andre Ayew and Angelo Ogbonna.
Such impressive transfer business so far this summer will raise questions over what West Ham fans can expect going into the new campaign. Last season, much of the club's downfall was due to inconsistencies at the back and failure to score goals - two issues Bilic has been quick to address through his summer aquisitions.
Should The Hammers manage to aoid such frustrating injury issues to their first-team players, they could be set for a promising season in England's top tier - as shown by their display against Werder Bremen.
Solid debut from Marko Arnautovic
The former-Stoke City winger made his first apperance for Slaven Bilic's side, delivering a promising performance. West Ham were by far the dominant team in the opening forty-five minutes, but fell behind to a goal from a set-piece. Caldirola rose high to tower above the defenders and steer the ball beyond Joe Hart, who also made his debut having signed on loan from Manchester City.
However, eleven minutes later West Ham's summer signing gave his new club a lifeline back into the match. A bright bit of play from Arthur Masuaku resulted in him delivering a threatening cross into the area. From there it was Arnautovic who reacted the fastest, much to the delight of his new manager.
It was thoroughly deserved goal for the Premier League outfit - and Arnautovic himself, who's promising link-up play with Masuaku was a highlight of the game. The Austrian almost scored a second goal, too, after unleashing an angled shot that Pavlenka managed to palm into the air. Unfortunately, Robert Snodgrass narrowly missed to headed rebound, steering the ball into the side netting from a tight angle.
Joe Hart enjoys a quiet first forty five for West Ham
The experienced English goalkeeper touched the ball just four times in the opening half - twice of which were to clear the ball up the field and get his side on the front foot and once due to Bremen's early goal. Steering in from a highly debatable free-kick was the German outfit's only attempt in the first-half, compared to West Ham's four shots.
It was hardly the most testing of halves for Hart, who will be looking to establish himself as the club's No.1 this season, having failed to make regular first-team apperaances for City.
The 30-year-old was almost set for a nerve racking penalty shootout on his debut when Toni Martinez helped complete a strong comeback from Bilic's side. It looked for all the world that the Betway Cup was to be determined from the spot until Yuning Zhang ensured West Ham came out second best on aggregate.
Ludwig Augustinsson steamed forward from the full-back position before steering the ball back to Zhang in the danger zone. Joe Hart was unable to reach the striker's shot as The Hammers narrowly missed out on the cup.
Thus, two years after winning the Betway Cup with a 2-1 win at the Boleyn Ground, Werder Bremen returned to London and repeated the same result.