Seventeen-time Grand Slam champion Roger Federer said he would go back to the drawing board after suffering a shock 6-4, 1-6, 6-2 defeat to Japan's Kei Nishikori in the third round of the Madrid Masters on Thursday.
Federer was competing for the first time since a two-month break from the tour and he admitted that he needs more practice before heading to the Rome Masters next week and eventually onto the French Open at the end of the month.
"I was lacking control from the baseline, and that pretty much carried through from start to finish," he told a press conference.
"Overall, I'm pretty disappointed with my play. I'm not sure how well Kei thought he played. I didn't think he had to play his very best either, which is even more disappointing.
"It doesn't change my mindset going forward. I'm going to go back to the practice court, train hard, and make sure I don't have these kind of days anymore."
The world number two had previously won the tournament in Madrid on three different surfaces and he didn't believe a switch back to the red clay had affected his performance after winning on the experimental blue clay surface last year, although he acknowledged that Nishikori had handled the windy conditions much better.
"Clearly the ball flies here and it's faster, so that makes it sometimes more tricky to find your rhythm.
"We're so accustomed to always finding that rhythm eventually, so it's even more disappointing if you never really find it, which was the case today.
"Credit to Kei. He got it done and was more solid in the wind. He played better than I did, so the better guy won today, that's for sure.
"I've been playing well here in Madrid in the past. Blue clay, red clay, indoors, doesn't matter. I've been very successful here, so clearly I'm disappointed and wish I could have done better this week.
"I was pretty upbeat after my first round match. I thought I was in the tournament; I was playing pretty well. In practice I was hitting the ball well, so this comes as a bit of a disappointment for me."
Nishikori, meanwhile, was understandably delighted to claim a first career victory over a man he described as his "idol", particularly on a surface on which he has struggled in the past.
"He was my idol, so, you know, to actually beat him, that was one of my goals for my tennis career. That it happens on clay is amazing because it's not my really favourite surface.
"I lost second or third round last week and I was struggling a little bit so I didn't have much confidence, but I played two good matches in the first and second round and to beat Roger, well, I'll need a couple days to celebrate."
And the 23-year-old recognised how important it was for him to start the third set strongly after being blown away in the second.
"He wasn't making many unforced errors in the second set and he was playing aggressive so I was a little bit worried.
"The first game in the third set was really important for me. I tried to hit to his backhand more in the third set and everything worked well.
"I was a little bit tight of course, but he didn't make many first serves in the third set and I was able to attack his second."