Top seed Andrey Rublev fought to save three match points, finding his way past Spaniard Bernabe Zapata Miralles 5-7, 6-1, 7-6 (7) to begin with a victory at the ATP Hamburg event.
Clay fan and two-time Roland Garros finalist Casper Ruud, seeded second, had to escape a tight situation to post a defeat of Argentine Sebastian Baez 6-3, 1-6, 6-3.
Rublev got out of jail on the northern German clay deep in the third set, saving the trio of match points in the tiebreaker to win in just under three hours.
“The feeling was that I was playing well and it was under control, but somehow I lost the first set and was frustrated,” he said.
“I came back and recovered mentally and won a really good second set.
“The third set was tough. I started to get tired and nervous, because the score is going to the tie-break and I didn’t have many chances to break him.”
Last week’s Bastad champion – winner of his last five matches – added: “The feeling was that he deserved to win. He was fighting like crazy from tough scores. It is amazing I was able to win.”
Rublev won the event in 2020, a year after reaching the final at the Rothenbaum Club.
Ruud’s defeat of Baez marked his 21st victory of the season, with the Norwegian struggling to secure a solid place in the field for the eight-man season finals in Turin in November.
“It was really tough,” Ruud said. “Sebastian is a great fighter. He has taken big steps in the past year, so it was always going to be a tough challenge.
“It takes a little time to adjust to new conditions. Today we had to play indoors under the roof, so it makes a difference on clay.
“It makes it a lot more humid and the balls are heavier, it took a while to adjust.
“I started well but the second set was not great, but I fought hard in the last and I am happy to be through.”
The Bastad finalist against Rublev four days ago will play for the quarter–finals against Cristian Garin after losing three of four matches against the Chilean.