Carlos Bacca scored a controversial penalty as AC Milan claimed a precious 1-0 victory at Sassuolo and ramped up the pressure on the Serie A top six.

The Colombian striker found the net in the 22nd minute of an end-to-end encounter at Mapei Stadium, but his spot-kick appeared to hit his standing leg on its way into the net and Sassuolo's players claimed the goal should have been ruled out.

The home side could have been ahead before Bacca's intervention had Domenico Berardi not blazed a penalty kick at the other end well wide and Sassuolo failed to capitalise on numerous other opportunities afforded them by some patchy Milan defending throughout the game.

Bacca was a constant threat in attack and he gave a performance that defied those who have criticised him in recent weeks, while Gerard Deulofeu and Suso continued their industrious link-up play, which has been vital to Milan's resurgence under Vincenzo Montella.

The result kept Milan within three points of sixth-placed Lazio and ended the club's unwanted record of having never won at Mapei Stadium in Serie A.

Deulofeu won a free-kick on the edge of the box as Milan pressed their hosts from the kick-off and Juraj Kucka failed to turn Suso's ensuing cross into the net when it seemed impossible to miss.

Berardi was felled in the box as he broke clear at the other end, but his penalty appeals were met with a yellow card for diving. But the home fans were appeased when Kucka pulled down Alfred Duncan and the referee pointed to the penalty spot.

However, Berardi wasted Sassuolo's chance to take an early lead by firing the spot-kick well wide of Gianluigi Donnarumma's goal, and Milan went straight back on the attack with Deulofeu twice drawing excellent saves from Andrea Consigli.

Milan took the lead in controversial circumstances when Alberto Aquilani was judged to have tripped Andrea Bertolacci in the box and Bacca's penalty appeared to go in via a deflection off his standing leg, but the goal was allowed to stand.

Bacca had a second ruled out for offside just before half-time after good build-up play from Deulofeu and Suso, who continued to cause Sassuolo problems after the break.

Gabriel Paletta's challenge on Matteo Politano drew further penalty claims from the home side, but appeals seemed to reflect a frustration with their failure to break down a packed Milan defence as much as any genuine hope of a favourable decision.

Sassuolo were dominant in the latter stages of the game with Politano tormenting the Milan defence, but the closest they came to an equaliser was a Berardi shot across the face of goal that Donnarumma palmed around the post.

Suso should have wrapped up the victory for Milan when substitute Lucas Ocampos put him clean through on goal, but his shot was brilliantly saved by Consigli, who then acrobatically saved a Cristian Zapata header. Consigli's heroics, though, were not enough to earn Sassuolo a share of the points.