Monfils, seeded 20th, stayed away from the showy highlight reel shots he has become known for and instead focused on a more workmanlike approach to stop the player dubbed "Baby Fed" for his all around game that resembles Swiss maestro Roger Federer.
Monfils had the only break chance in a tight opening set and did not waste the opportunity going up 6-5 and then holding serve for a 1-0 lead.
After trading breaks in the second the set went to a tiebreaker where the 23-year-old Bulgarian charged ahead 6-4 and looked poised to level the match until Monfils swept the next four points to grab control.
The lanky Frenchman closed out the contest with another break when Dimitrov double-faulted, sending him back to the US Open quarter-finals for the first time since 2010.
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