John Isner and Sam Querrey moved into the US Men's Clay Court Championship quarter-finals with straight-sets wins.
Isner, the top seed, sent down 24 aces in a 7-6 (7-2) 7-6 (7-4) win over fellow American Denis Kudla on Wednesday.
The big-serving world number 15 is the 2013 champion and 2012 runner-up at the ATP 250 event in Houston.
Isner made it two wins from as many meetings with Kudla as his serve did the damage.
Next up for Isner is Chung Hyeon, who battled past American Tommy Paul 5-7 6-2 6-2 in a clash between two teenagers.
Querrey had a far more straightforward win, taking just 50 minutes to crush Benjamin Becker 6-3 6-3.
The fifth seed and two-time runner-up broke three times and served 13 aces to close out an easy win.
Awaiting Querrey in the last eight is Juan Monaco, who overcame French second seed Benoit Paire 6-3 7-5.