Stan Wawrinka’s comeback tournament ended with a second-round loss to Tennys Sandgren at the Australian Open.

The 2014 champion was back in action for the first time since Wimbledon after undergoing surgery on his left knee and only decided that he would definitely play on Saturday.

After pulling out of all his scheduled warm-up events, Wawrinka sounded decidedly pessimistic about his chances but fared better than expected in a first-round victory over Ricardas Berankis.

However, he never looked comfortable against American Sandgren, ranked 97, and lost comprehensively 6-2 6-1 6-4.

Of more concern was the degree of pain Wawrinka seemed to be feeling in his knee, with the 32-year-old wincing and flexing the joint, which bears a large scar.

While this was a tough day for Wawrinka, it was a landmark one for 26-year-old Sandgren, who had never won a grand slam match prior to arriving in Australia and will face young German Maximilian Marterer in the last 32.