Alex de Minaur was again stunned by Marcos Giron as the third seed crashed out of the Sofia Open in the second round. 

Following his success over De Minaur at the Moselle Open last week, Giron beat the world number 26 once more as he battled to a 7-6 (7-5) 7-6 (7-2) victory in two hours. 

The unseeded American, appearing for the first time in Sofia, rallied from a break down in the second set to reach an ATP Tour quarter-final - where he will meet John Millman - for the fourth time this season. 

Millman, who is seeded eighth, lost the first set against qualifier Illya Marchenko but recovered well to comfortably triumph 5-7 7-6 (7-0) 6-3. 

However, it was far more straightforward for the other favourites, with top seed Jannik Sinner avoiding a second-set blip to defeat Egor Gerasimov 6-2 7-6 (7-3) and Gael Monfils getting a walkover against Ilya Ivashka. 

Number five seed Filip Krajinovic coasted past fellow Serbian Laslo Djere 6-3 6-0 in just over an hour to set up a quarter-final tie with Kamil Majchrzak. 

In Thursday's other match, world number 56 James Duckworth smashed Benoit Paire 6-4 6-4 in just an hour and 15 minutes to collect his 11th win in his past 12 outings. 

Duckworth, who reached his first ATP Tour final in Nur-Sultan last week, will now challenge defending champion Sinner in the next round.