Novak Djokovic admitted on Friday he needs to raise his game considerably ahead of Roland Garros next month after suffering a shock quarterfinal defeat by Dusan Lajovic in Banja Luka.
The world No 1 was far from his best as he lost 6-4, 7-6 (8/6) to the 70th-ranked Lajovic, having previously dropped just four games across two previous meetings with his Serbian compatriot.
"I was many levels below what I want," said Djokovic, who converted only one of 16 break points and let three set points slip in the second-set tie-break.
"Playing like that, I can't win against opponents who are so solid on this surface. But what can I do? It's simply sport. I was trying but it wasn't working.
"I didn't feel very good physically on court. My legs were slow, I missed a lot of balls. I played well at times, but generally well below standard."
With Rafael Nadal's status for Roland Garros uncertain and Carlos Alcaraz also working his way back from injury, Djokovic is targeting a record 23rd men's Grand Slam title at Roland Garros.
But his form since returning to action after missing tournaments at Indian Wells and Miami last month over his refusal to get a Covid-19 vaccination is cause for concern.
He has also alluded to a problem with his elbow, which hampered him during his last-16 loss in Monte Carlo last week and was "not in ideal condition" in Banja Luka.
DJOKOVIC STILL FINDING HIS FEET
Djokovic is a two-time Roland Garros champion, finishing runner-up on four occasions as well, and hopes to shake off the rust with two key warm-up events still on the schedule in Madrid and Rome.
"For Roland Garros, it's not a secret. It's the tournament where I want to play my best tennis and I'm working on it," he said.
"The conditions there are completely different to those in Monte Carlo and Banja Luka. There are still quite a few weeks to play and to train.
"In past seasons (on clay), it's always been a bit like that: a bad start, slow, and then a better game towards the end of the clay. I hope that will be the case this time too."
As for Lajovic, whose lone ATP title came on clay in Umag in 2019, he will take on Miomir Kecmanovic – a 7-5, 6-0 winner over Jiri Lehecka – in the last four on Saturday.
"I'm overwhelmed," said the 32-year-old Lajovic. "It's the biggest win of my career. Beating him (Djokovic) is something I didn't even think was possible, but it happened."
Andrey Rublev secured his place in the semifinals after recovering from a poor start to beat Bosnian wild card Damir Dzumhur 7-5, 6-3.
Rublev, who won his first Masters title in Monte Carlo last week, trailed the 202nd-ranked Dzumhur 5-2 in the opening set before saving a set point and winning five games on the bounce.
The second seed was again under pressure as he fought off four break points early in the second set, but steadied himself once more and grabbed the key break in the fifth game.
"We've always had tough battles and today was the same. I was lucky I was able to come back," said Rublev, now unbeaten in five matches against Dzumhur.
Rublev's reward for extending his winning run to seven matches is a semifinal against Slovakia's Alex Molcan, the world number 73 who beat Laslo Djere of Serbia in three sets.