Mercedes motorsport boss Toto Wolff has admitted that they pushed Nico Rosberg's power unit too hard in the Italian Grand Prix.

After a poor start, Rosberg was running third in Sunday's race and closing on Sebastien Vettel when his engine let go with two laps remaining.

It was the German's - and Mercedes' - first DNF of the season and afterwards Wolff said they should have known better. Indeed the power unit had already done five races, Rosberg having to revert to it ahead of qualifying the day before when the upgraded unit developed an issue.

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"Nico climbed back through the field thanks to strong pace and some great work on the pit wall, when he made an aggressive early stop to undercut both Williams cars in front of him - with a great stop from the boys. That put him in free air and he started a long charge to hunt down Vettel in front. P2 looked possible and Nico was pushing hard to close in - we pushed the power unit very hard and, in hindsight, too far for the high mileage it had," Wolff confirmed.

"It's a bitter pill to lose a podium finish just three laps from the end and with P2 in your sights."

The result leaves Rosberg a sizeable 53 points - more than two races wins - behind team-mate Lewis Hamilton in the Drivers' Championship, with seven races remaining, although the German has vowed not to give up.

Meanwhile, Mercedes executive director technical, Paddy Lowe was apologetic for the power unit problems on both race day and the day before.

"The weekend first started to unravel for Nico on Saturday with the failure of a component which contaminated his engine, forcing him to run a Power Unit which had already competed in five race weekends," Lowe added.

"The power loss from the age of the engine likely cost him a front row grid slot in qualifying and had then clearly been pushed too far in undertaking a sixth race on Sunday. He produced a fantastic recovery drive after a tough start and deserved a result, so our apologies once again to him. We will learn a lot of lessons from this weekend to take into the coming races."