Philipp Kohlschreiber survived a second-set wobble before finally overcoming Alejandro Falla at the Heineken Tennis Open in Auckland.
The second seed from Germany reached the quarter-finals with a 7-6 (7-4) 4-6 6-3 victory over the Colombian.
Top-seed David Ferrer also needed three sets to progress - the Spaniard beating Yen-Hsun Lu 6-4 2-6 6-3.
Kohlschreiber and Ferrer are joined in the next round by fellow top-ranked players Sam Querrey and Tommy Haas.
Querrey, the No 4 seed, saw off the challenge of Olivier Rochus 7-5 6-3, while the third-ranked Tommy Haas defeated Igor Sijsling 6-3, 6-4.
Haas, a former winner of the title in Auckland, will now face wildcard Gael Monfils after the Frenchman saw off Greg Jones 6-4 6-2.
Eighth-seed Thomasz Bellucci was a notable casualty as he suffered a 6-3 7-5 loss to Lukas Lacko.
However Xavier Malisse and Jesse Levine both reached the last-eight with straight-sets victories.
Malisse triumphed 7-6 (8-6) 6-4 against Santiago Giraldo, while Levine beat Brian Baker 7-5 6-4.
More to follow...
