first match since the US Open, del Potro was upset by world No. 189 Édouard Roger-Vasselin in straight sets at the Rakuten Japan Open Tennis Championships in Tokyo. He then lost his second straight match to Melzer in the second round at the Masters 1000 event in Shanghai, retiring while trailing in the second set. This retirement caused concerns over the length of the tennis season. He had to retire again in the Paris Masters quarterfinals when down 0–4 to Radek Štěpánek due to an abdominal injury. In November, del Potro competed in the ATP World Tour Finals, where he lost his first round-robin match against Andy Murray, but he managed to defeat Fernando Verdasco in his second match to keep his hopes alive. After defeating Roger Federer in the following match, he qualified for the semifinals, ousting Murray by the slimmest possible margin of one game. He defeated Robin Söderling in the semifinals, before losing to Nikolay Davydenko in the final. Del Potro finished 2009 as the youngest player in the top 10, top-ranked Argentine, and highest-ranked South American for the second consecutive year. 2010: First wrist injury, out of top 250 Del Potro started his 2010 season at the AAMI Kooyong Classic in Melbourne, Australia with a win over Croatian world No. 24 Ivan Ljubičić. On 11 January, he moved up to a career high world No. 4. He was scheduled to face Frenchman Jo-Wilfried Tsonga on day 2 of the Kooyong Classic exhibition tournament, but withdrew due to a wrist injury. He came into the 2010 Australian Open with the injury not healed, and took a month off after the event. In the fourth round, he fell to eventual semifinalist Marin Čilić. Following the Australian Open loss, del Potro missed several tournaments, including the Masters tournaments at Indian Wells and Miami, which were touted as potential return dates, due to the persistent wrist injury. Even though he withdrew from the Monte-Carlo Rolex Masters, he regained the world No. 4 ranking, due to Murray's early exit in the second round. He then withdrew from Barcelona and the Rome Masters. On 4 May, del Potro took the option of having an operation to fix the injury. On 19 May, del Potro said he would not defend his US Open title, but if all went well, he would appear after the event, targeting the Paris Masters as a possible comeback.