Rafael Nadal had to dig deep to see off a player of "unbelievable potential" as the world number three booked his place in the quarter-finals in Indian Wells.
Nadal, who is returning to action at this tournament after several weeks on the sidelines with a knee injury, required three sets to see off giant American John Isner.
The defending champion was looking to avoid joining world number one Roger Federer through the exit door, and survived a scare against 6ft 9in Isner to earn a 7-5 3-6 6-3 win.
"Today was a really difficult match," said Nadal. "John is a big player, very difficult to play, and has unbelievable potential. So for me it is a very important and very good victory."
Nadal will now meet the Czech Republic's Tomas Berdych, who beat Viktor Troicki of Serbia 6-1 6-3.
After beating world number one Federer yesterday, Marcos Baghdatis failed to build on that victory as he crashed out to 18th-seeded Spaniard Tommy Robredo 7-5 0-6 6-4.
Second seed Novak Djokovic was the major shock of the round as he was beaten 7-5 6-3 by Ivan Ljubicic.
Despite the disappointment of defeat, Djokovic maintained he could take some positives from his efforts.
"I am not happy with the overall performance that I had in this tournament, because I know I could have played better and could have done better," the Serbian said.
"But, under decent circumstances, I still made it to the fourth round."
Andy Murray eased into the quarter-finals after fourth-round opponent Nicolas Almagro was forced to retire with an ankle injury.
Next up for Murray is a tricky clash with sixth-seed Robin Soderling, who defeated Jo-Wilfried Tsonga 6-3 6-4 to reach the last eight.
In the women's draw, second seed Caroline Wozniacki was pushed to a third-set decider against China's Zheng Jie before sealing a semi spot.
The Dane was forced to fend off four break points in the final set before winning 6-4 4-6 6-1.
Next up for Wozniacki is Poland's Agnieszka Radwanska, who booked her place in the semis with a 6-4 6-3 win over Elena Dementieva.