Former US Open champion Stan Wawrinka on Saturday won the second-tier Challenger tournament in Prague, on his return to action after a six-month break because of the coronavirus pandemic but admitted: "I'm not at my best yet". Wawrinka, the 2016 US Open winner, has elected to skip this year's Grand Slam in New York citing the "health situation" in the city and instead focus on Roland Garros which starts on September 27. World number 17 Wawrinka defeated 253rd-ranked Aslan Karatsev of Russia 7-6 (7/2), 6-4 in the Prague final on clay. The three-time Grand Slam champion was playing in his first event since reaching the quarter-finals at Acapulco in February. He won the last of his 16 ATP Tour titles at Geneva in 2017. "It was the best match of the week and the level was good. The focus was there, I was serving well and I'm really happy to get the trophy today" said Wawrinka. "It was nice to come back here and play a Challenger at the Prague Open, especially after so many months away." He added: "I feel good, but I know I'm not at my best yet. That's the reason why I came here. I wanted to get some matches." The Swiss veteran will stay in the Czech capital for another Challenger event next week. ig/ll/mw/nr/dj