Novak Djokovic described his shock defeat to Taro Daniel as "like the first match I ever played on the Tour" as his return ended early at the Indian Wells Masters.
Former world number one Djokovic was playing his first match since the Australian Open due to a elbow problem that required surgery.
But he went down 7-6 (7-3) 4-6 6-1 to the Japanese qualifier in the second-round match, leaving the 30-year-old to lament a disjointed performance.
"For me it felt like the first match I ever played on the Tour," said Djokovic. "Very weird. I mean, I just completely lost rhythm, everything.
"I just struggled also a little bit with the health the last couple of weeks.
"I was grateful to be out on the court after surgery that quickly. But at the same time, I just didn't feel good at all.
"Obviously having only played a couple of matches in nine months, you're still, in a way, battling inside of your mind whether you're fit or not.
"And even though you don't have pain, you're still thinking about it, because it's been something that I have been feeling and dragging for over two years."
It marks the first time Djokovic has lost back-to-back Tour matches since the 2011 ATP Finals - though he did lose consecutive contests at the 2012 Olympics - but the Serbian was able to take positives from the defeat.
"I was not even supposed to be here because of the surgery that was only five, six weeks ago. But I recovered very quickly, and I got myself ready," he added.
"I'm just happy that I managed to recover that quickly after surgery and just get out on the court."