Andy Murray reached his first quarter-final in six months on Thursday as the unseeded Briton defeated Alexander Bublik 6-3, 7-6 (7/4) at the Stuttgart grass court tournament.
Murray won the opening set against his Kazakh opponent but had to come from 5-2 down in the second to clinch the win.
The former world number one said his confidence is improving after defeating Bublik in one and three-quarter hours.
"It's nice to be back at this stage," said Murray who will take on top seed Stefanos Tsitsipas for a place in the semi-finals.
"This was a solid win and I'll try and push through to the semis.
"When I was down in the second set it was frustrating, I was thinking of what I could do differently.
"He hit some great shots - but some that you wouldn't teach. The multiple drop shots were unexpected."
Murray's last appearance in the quarter-finals was in January when he reached the final in Sydney.
A win over Tsitsipas on Friday would push the 35-year-old closer to a return to the top 50 for the first time in more than four years.
Tsitsipas schooled Switzerland's former French Open champion Dominic Stricker 6-3, 6-4 in a match interrupted by rain with the Greek up a set and 2-0.
World number five Tsitsipas won his only previous match with Murray last August in the US Open first round in a five-set duel.
Playing on a wild card, Tsitsipas managed only four aces against nine for world number 200 Stricker but broke the 19-year-old twice.
"My game is built for grass courts, I can 100 per cent have good results on this surface," Tsitsipas said. "But it might take a bit of time.
"I want to get the most out of my game and push it to the limit."
The 23-year-old, who has lost in the first round in three of four Wimbledon appearances, said Murray will be a tough opponent on the German grass courts.
"Andy is one one of the best grass players. He's been out injured but he's been getting some good wins against some of my peers," the Greek said.
"His game is absolutely there, he's one of the favourites here.
"He's had a lot of grass battles and a lot of good wins."
Nick Kyrgios needed almost two hours to defeat Nikoloz Basilashvili of Georgia 6-7 (4/7), 6-4, 6-3 in chilly evening temperatures after another rain delay.
The Australian, who says he is limiting his season to 10 or 12 tournaments, was proud of how he fought back.
"I'm proud of how I played, I've had to deal with a lot off-court (airline baggage problems, rain delays)," he said.
"It was a tough day, but I was resilient, I put my head down, it was not easy.
"Basilashvili is a tough opponent, he's ranked 25 for a reason."
Kyrgios will play on Friday against Hungarian Marton Fucsovics, a winner over Hubert Hurkacz 7-5, 6-7 (7/9), 6-3.