Top seeds John Isner and Gael Monfils reached the Citi Open quarter-finals as Bernard Tomic suffered a surprise loss.

Isner, a three-time runner-up in Washington, is on yet another run after a 7-6 (7-3) 6-2 win over Marcos Baghdatis in the third round.

The American sent down 15 aces to advance at the ATP 500 event played on hard courts, setting up a last-eight clash against Steve Johnson.

The fifth-seeded Johnson was too good for qualifier Ryan Harrison 6-4 6-4.

Runner-up in 2011, Monfils eased through courtesy of a 6-2 6-3 win over Croatian 16th seed Borna Coric.

Next up for the Frenchman is Sam Querrey, who overcame Alexandr Dolgopolov 7-6 (7-5) 6-3.

Tomic was the highest seed to depart as the Australian was rather convincingly beaten by Ivo Karlovic.

The big-serving Croatian sent down 21 aces and lost just 10 points on serve in a 7-6 (7-4) 6-3 victory.

Karlovic will meet Jack Sock, who claimed a 6-1 7-5 win over Daniel Evans.

In the other quarter-final, Benoit Paire and Alexander Zverev will do battle after wins over Gilles Muller and Malek Jaziri respectively.

Paire beat 2004 runner-up Muller 6-2 3-6 7-6 (7-4), while Zverev edged Jaziri 6-2 5-7 6-2.