Mardy Fish's latest return to action ended in disappointment as he lost to Michael Russell at the BB&T Atlanta Open.
The 31-year-old has been plagued by health and fitness problems over the past year, with Fish having to contend with a heart issue.
Fish, a former top-10 ranked player, has played in just two tournaments this season, with his last appearance coming in a low-profile Challenger in April.
However it looked like he could progress in Atlanta as he took the first set only for Russell to hit back to record a 4-6 6-2 7-5 victory.
Russell said on the ATP website: "I played fantastic. Mardy's such a great competitor. I thought he played really well, first match back in four months.
"I thought it was a really high quality match. Both of us, on big points, were coming up with great shots. It's a positive for both of us going into the summer."
Former US Open and Wimbledon champion Lleyton Hewitt had to dig deep to beat Rhyne Williams, with the seventh seed eventually coming out on top 7-6 (8/6) 6-4.
Third seed Ivan Dodig also survived a scare as he edged past Ricardas Berankis 6-1 6-7 (3/7) 6-3 to set up a clash with Hewitt in the quarter-finals.
The first-round action was completed as Christian Harrison and James Blake reached the last 16, along with Matthew Ebden who had taken the first set 6-2 in his tussle with Ivo Karlovic when the Croatian retired, citing fatigue.