Kyle Edmund was knocked out of the Vienna Open by Spain's Fernando Verdasco.
The British No.1 claimed a European Open win in Antwerp on Sunday for his first trophy on the main tour, before following it up with a first round win over Diego Schwartzman.
However, Verdasco procied too much for Edmund who succumbed to a 6-4 3-6 6-3 defeat in a close encounter.
In a game that lasted one hour and 55 minutes, the Spaniard had the better of three breaks to start the match and held on to take the opening set. Edmund did offer a response breaking serve at the start of the second and levelling the match, but one break proved the difference in the decider and it was Verdasco who grabbed it.
He now moves through to a quarter-final with either Gael Monfils, who defeated American fourth seed John Isner 6-4 6-4.
Edmund heads to Paris for the final Masters tournament of the season, which he would need to win to give himself a chance of qualifying for the ATP Finals in London.
Elsewhere, Dominic Thiem will face Kei Nishikori in the quarterfinals after beating American Sam Querrey 6-4, 6-4 on Thursday.
The 25-year-old Austrian lost only four of his service points during the match, which lasted 78 minutes, after saving three break points at 3-2 in the second set.
"It was a good match," Thiem told journalists.
"I think I was returning quite well. I still felt quite a lot of pressure on my own service games because he was serving really well and he has such a dangerous game. So I knew that if I got broken back once, that the match would be completely open again. So I'm very happy that I made it in two sets."
He added: "Especially for us tennis players, we don't have many chances to play at home. It's a very unique and nice feeling that are the people are behind me, so I enjoyed every second of it."
The win was the top seed's 50th victory of the 2018 tennis season.
Nishikori earned his place in the quarterfinals after beating Russia's Karan Khachanov 6-2, 6-2 with two service breaks in each set.