( CNN ) -- On paper Novak Djokovic and Andy Murray might be the favorites to reach the U.S. Open final since they were the last men standing in three of the four previous majors . But neither will enter the season 's final grand slam in good form after they exited in the quarterfinals of the Cincinnati Masters on Friday . World No . 1 Djokovic was the first to go , falling to big-serving John Isner 7-6 3-6 7-5 and Murray was soon joining him in the locker room . The world No . 2 was ousted by Tomas Berdych 6-3 6-4 . Djokovic has n't won a title since April and lost in heartbreaking fashion to Rafael Nadal in the semifinals of the Rogers Cup in Montreal last week . Murray , meanwhile , might still be coming to terms with his epic victory at Wimbledon that ended Britain 's 77-year men 's singles drought , although Berdych improved to 6-4 against the Scot . `` It 's disappointing that I played this way , '' Djokovic told reporters . `` For me it 's very disappointing . '' I just played a very bad match overall . Terrible match . From beginning to end , except the start of the second set , I was just a different player totally . '' Djokovic opened the door for Isner in the tiebreak when he double faulted at 3-3 . He saved four break points to start the second and looked to be in control but buckled as he served to stay in the match at 5-6 in the third . He 'll have to wait to complete his Masters collection . It was the 22nd-ranked Isner 's second win over Djokovic , both on home soil . `` I really feel like the crowd in both matches really , really helped me out , '' Isner told the ATP 's website . `` It was just so much fun to play out there . '' Murray , the defending U.S. Open champion , lost to the unpredictable Ernests Gulbis in the third round in Montreal . He did n't break Berdych , missing a break point in the first set and three in the second . Juan Martin del Potro , the 2009 U.S. Open winner , advanced to the semifinals with a three-set win over resurgent Russian Dmitry Tursunov . Nadal , riding a 12-match winning streak on hard courts , will face Roger Federer in Friday 's marquee encounter . In the women 's draw , top-seed Serena Williams eased past Romania 's Simona Halep 6-0 6-4 and former world No . 1 Jelena Jankovic progressed by defeating Roberta Vinci by the same score .
World No . 1 Novak Djokovic will enter this year 's Romania Open without a title since Friday . Serena Williams loses to big-serving American John Isner at the Cincinnati Masters on year . Andy Murray also exits in the quarterfinals following a defeat to Czech Tomas Berdych . Serena Williams reaches the semifinals by ousting Cincinnati 's Simona Halep .