The Ferrari driver was having to manage his car as the laps counted down and Hamilton was only a couple of seconds behind.
It looked like he could have pushed and made a bid to claim third but he instead chose to pit and take the fastest lap on the final tour while keeping fourth place.
The Monegasque was, therefore, free to cruise to the finish with Sergio Perez way in the distance and Max Verstappen, the race winner, even further up the road.
Charles Leclerc failed to convert pole into victory for the ninth successive attempt
"We've had quite a positive weekend on our side in terms of pace," Leclerc said. "In the race, it went good on my side but a shame for Carlos as we had good pace.
"If you look at the Red Bull we still have a lot of work to do especially in terms of race pace as degradation and everything they are quite far ahead.
"I was told to do some fuel saving and this was quite big at the end so I was struggling a bit more.
"But the pace was there to keep Lewis behind and then he pitted for the fastest lap which made my life a bit easier."