Top seed Dominic Thiem beat Aljaz Bedene 7-5 6-4 to book a place in the quarter-finals of the Qatar Open while fellow seeded players fell in the second round of the tournament in Doha on Wednesday.
Slovenian Bedene saved 12 out of 15 break points to push the Austrian but the world number five survived the test and is the only seeded player apart from Frenchman Richard Gasquet, who won the event in 2013, not to exit in the opening rounds.
But world number 31 Gasquet, the fifth seed, also departed the tournament, losing to Greece's Stefanos Tsitsipas in straight sets later on Wednesday, 6-3 6-4.
Video - Highlights: Monfils sees off Struff in Doha
Tsitsipas now faces Thiem in the next round.
Seventh-seeded Fernando Verdasco was defeated 6-4 3-6 6-4 by Russian youngster Andrey Rublev while eighth seed Feliciano Lopez suffered a shock 6-4 7-6(2) loss to Bosnia's Mirza Basic, who is ranked 138 in the world.
The Spanish duo join high-ranking players Pablo Carreno Busta, Tomas Berdych, Albert Ramos-Vinolas and Filip Krajinovic, all of whom exited the tournament in the early stages.
In the quarter-finals, Rublev, 20, will face Croatia's Borna Coric, who ousted Carreno Busta in the first round, while Basic will take on Guido Pella after the Argentine overcame Stefano Travaglia 7-6(4) 6-3.
The last quarter-final will see German Peter Gojowczyk, who knocked out Krajinovic, take on France's Gael Monfils, who beat Jan-Lennard Strugg 6-3 6-1 6-3.