Belgrade - Novak Djokovic was denied his first title of the year on Sunday, the world number one admitting he "ran out of gas" in a three sets defeat to Russia's Andrey Rublev in the final of the Serbia Open.
Second seed Rublev won 6-2, 6-7 (4/7), 6-0 against the top seed who had been looking to regain winning form before his French Open title defence next month.
The Belgrade event in his hometown was only Djokovic's third of 2022 after he was deported from Melbourne - and denied the chance to defend his Australian Open title - after entering the country unvaccinated.
However, despite the 20-time Grand Slam winner being let down by his lack of physical form, he remains upbeat for his bid to capture a third French Open crown.
"Things are progressing slowly but surely, Paris is the big goal and hopefully by Paris I'll be ready," said the two-time Serbia Open winner.
The 34-year-old, who lost in the quarter-finals in Dubai and suffered a shock second-round defeat in Monte Carlo, battled past Laslo Djere, Miomir Kecmanovic and Karen Khachanov in three sets before the court time caught up with the top seed against Rublev.
"I have to look at the positives, playing the final in front of my home crowd, it was unfortunate that in the third set I ran out of gas and couldn't deliver more of a fight," said Djokovic.
"After four three-set battles I can say that I am tired but also pleased that I managed to win the matches prior to this one.
"I think that will serve me for the continuation of the clay court season."
Djokovic got off to a bad start, dropping serve twice, to lose the first set after half an hour.
Bouyed by the support of the 8,000 crowd, Djokovic fought back in a marathon second set which lasted just over an hour, levelling in the tie-break despite wasting six set points, before running out of steam in the third.
Rublev captured his third title of the season, days after blasting Wimbledon's ban on Russian and Belarusian players as "complete discrimination".
Wimbledon banned all Russian and Belarusian players from this summer's Grand Slam tournament due to the invasion of Ukraine.
It was a decision condemned by the ATP and WTA as well as a host of players including Djokovic who described the sanction as "crazy".
Rublev has now equalled Spaniard Rafael Nadal for the most tour-level titles in 2022, having also clinched crowns in Marseille and Dubai in February.
"He was for sure not in his high level, maybe middle level," said Rublev of Djokovic.
"In the third set I was really lucky that he couldn't break me and that he was really tired."