Isner downs del Potro to set up final with Nadal August 17, 2013 -- Updated 2320 GMT (0720 HKT) John Isner claimed another prize scalp in the Western and Southern Open semifinal beating Juan Martin del Potro in three sets. John Isner beats del Potro to book place in second Masters 1000 final American saves match point before prevailing in three sets Rafa Nadal beats Tomas Berdych in second semifinal 7-5 7-6 (CNN) -- John Isner has continued his remarkable run at the Western and Southern Open in Cincinnati defeating Argentina's Juan Martin del Potro to set up a meeting with Rafa Nadal in Sunday's final. The unseeded American, who beat World No.1 Novak Djokovic in the quarterfinals on Friday, rose to the challenge again on Saturday downing del Potro in three sets 6-7 7-6 6-3. Having lost the first set on the tiebreak, Isner was in danger of losing in straight sets as the World No.7 served for the match at 5-3 in the second set. All looked lost when the big Argentine reached match point, but it proved to be a turning point in the match rather than the end of it. Del Potro double-faulted handing Isner a lifeline which he grabbed with both hands, first forcing a tiebreak before going on to take the third set with relative ease to reach the second ATP World Tour Masters 1000 final of his career. "I've been winning a lot of matches this summer," Isner said, ATPWorldTour.com reported. I feel like this tournament here is where I'm really starting to put it all together. I've beaten three Top 10 guys in a row. For me to do that, I have been playing well, really in pretty much all facets of my game. There's definitely some stuff I can always improve on, but I do think I'm playing well," he added. Isner's reward is a match up against Rafa Nadal. The World No.3, who beat Roger Federer in a thrilling quarterfinal on Friday evening, found his semifinal opponent Tomas Berdych a little easier to overcome -- the Spaniard prevailing 7-5 7-6 against the World No.6. In the women's draw, Serena Williams takes on China's Li Na in the first semifinal with Serbia's Jelena Jankovic playing Victoria Azarenka from Belarus.