Monte Carlo - Japan's Kei Nishikori fought back from a set down to see off Czech 12th seed Tomas Berdych on Monday and reach the Monte Carlo Masters second round.
In a battle of two former Grand Slam finalists, Nishikori raced through the final two sets to progress with a 4-6, 6-2, 6-1 victory.
The former world number four, who is now ranked 36th, missed a large part of last season with a right wrist injury and started his 2018 campaign in American second-tier Challenger Tour events.
But he was close to his best against Berdych, despite making a slow start.
Berdych moved into a 4-1 lead en route to the opening set, but Nishikori moved into another gear and claimed four straight games to level the match.
The deciding set was even more one-sided, as two breaks to love helped the 28-year-old to his best win of the season so far.
Nishikori, playing in the tournament for the first time in six years, will take on Russian youngster Daniil Medvedev in round two.
Earlier on Monday, American Jared Donaldson launched into an angry tirade at umpire Arnaud Gabas while squaring up to the Frenchman over a line call during his defeat by Albert Ramos-Vinolas.
The 21-year-old petulantly insisted a supervisor was called to check the mark, saying: "I can call the supervisor whenever I want."
He then sarcastically apologised, saying he was "sorry" to hurt Gabas' feelings.
Ramos-Vinolas, who lost last year's final to Rafael Nadal, was leading by a set and a break at the time and went on to win 6-3, 6-3.
French veteran Julien Benneteau bowed out of his final appearance in Monaco at the first hurdle with a straight-sets defeat by Borna Coric, while Russian Andrey Rublev edged out Robin Haase 7-5 in a third set.