Mercedes driver Nico Rosberg won the race by a stout 15.070 seconds over his Brackley team-mate Lewis Hamilton, further tightening the championship battle.
Rosberg’s second straight victory lopped seven points from Hamilton’s advantage, thinning the margin to just two points. The victory was Rosberg’s 21st career Formula One victory, his seventh of the season and his first at Monza.
Grosjean overcame a five-place grid penalty for a gearbox change that turned his 12th-place qualifying effort into a 17th-place starting spot for the Banbury team.
Despite the setback, Grosjean made the most of his start, rallying to 13th after the first lap. He passed the Manor of Pascal Wehrlein on lap two to take 12th, from there, Grosjean settled in for a long haul, at least by Formula One standards.
He was the last driver to pit, going 28 laps before swapping the Pirelli P Zero Yellow soft tires he used to start the race for a set of Red supersofts. Grosjean then managed those tires for the next 25 laps, with his one-stop strategy allowing him to finish 11th even while holding off the surging McLaren of Jenson Button in the closing laps.
Gutiérrez began the 53-lap race in tenth place thanks to a strong qualifying performance on Saturday. It was rendered moot, however, when a slow start saw the field zoom around him, dropping him all the way to 20th.
Gutiérrez recovered a bit to climb to 18th by lap seven. He made his first pit stop at the end of lap 16, changing from the Red supersofts he first used in qualifying to a new set of Yellow softs. By lap 24, Gutiérrez had climbed to 15th.
He made his second and final stop at the end of lap 34, grabbing a used set of Red supersofts that helped him finish 13th and keep the 14th-place McLaren of Fernando Alonso at bay.
Fourteen rounds into the 21-race Formula One schedule, Haas remains eighth in the constructor standings with 28 points. There was no movement on either side of the American squad, as seventh-place Toro Rosso and ninth-place Renault failed to score points.