By Clive Leviev-Sawyer of the Sofia GlobeGrigor Dimitrov’s run at the US Open came to an end in the fourth round with a loss to Frenchman Gael Monfils in straight sets 5-7, 6-7, 5-7 on September 2.Dimitrov came into the match favoured, but there was little to separate the two players early on, as both held service comfortably early on. With most points decided by quick rallies, spectators in the Arthur Ashe stadium that anticipated a show between two of the most entertaining players on the ATP Tour would have been disappointed by the first set.With Dimitrov’s service beginning to slip after a strong start, Monfils took the first set after making several big winners to break service at his first opportunity, half an hour into the match.Prone to emotional outbursts, the Frenchman played unusually calm, but his fiery temperament showed up in the second frame, when Monfils started remonstrating loudly with himself after allowing Dimitrov to break back to even the set at 4-4. Before that, Dimitrov had several opportunities to take the lead as Monfils was clearly struggling with his grip, but failed to take advantage.With Monfils still fuming, a visibly calmer Dimitrov had a chance to put pressure on his opponent, but repeatedly left Monfils off the hook with ill-timed unforced errors. In the tie-break, with two set points, Dimitrov’s errors became crucial, as he let slip a 6-4 advantage to lose 6-8 in the end.In the third set, Dimitrov once again could have brought himself back into the match as the Frenchman appeared to struggle with the high heat and humidity, struggling for breath between points, but the Bulgarian let every opportunity slip past, as Monfils repeatedly dug deep enough to produce a strong serve or a winner to avoid conceding a break.In the end, Dimitrov’s ill-timed unforced errors proved crucial and he lost the match on a double fault when serving to push the frame into a tie-break. Monfils will play second-seed Roger Federer, who defeated Spain’s Roberto Bautista Agut in straight sets (6-4, 6-3, 6-2), in the quarterfinals.In another fourth-round match played at the same time, Croatia’s Marin Cilic overcame another Frenchman, Gilles Simon, in a gruelling five-setter by a score line of 5-7, 7-6, 6-4, 3-6, 6-3. Having lost all the previous four matches against Simon, Cilic looked set for another defeat early on, despite his opponent requiring a medical time-out for treatment on his back midway through the first set.The Croatian recovered admirably to take the next two frames despite numerous unforced errors, although he did compensate somewhat by scoring more winners than Simon.Cilic will next play sixth-seed Tomas Berdych from the Czech Republic, against whom he has a 3-5 career record. The Croatian did win their last encounter, in the third round of Wimbledon earlier this summer.Meanwhile, top seed Novak Djokovic of Serbia will play his quarterfinal match against Britain’s Andy Murray on September 3, reprising the 2012 US Open men’s final. Djokovic leads 12-8 in their previous meetings, including 3-2 in Grand Slams, with the two losses coming in the 2012 US Open final and the 2013 Wimbledon title match.