British number four Jack Draper progressed to the quarter-finals of the Sofia Open with a shock victory over Italian top seed Lorenzo Musetti in Wednesday's second-round match.

The world number 82 - who sits 55 places lower than his fellow 21-year-old in the ATP rankings - followed up his convincing opening victory over Maximilian Marterer by defeating Musetti 7-5 6-2 in one hour and 48 minutes.

Musetti did not manage a single ace against Draper, who in turn sent seven the Italian's way while winning 89% of his first-serve points, as well as saving five of the six break points he faced on the day.

"Lorenzo is an amazing player, one of the top young players in the world, so I knew it would be a real challenger," Draper said on the court after advancing to the quarter-finals.

"I started off a little slow but after that I found momentum and am proud of the way I played. I am feeling really confident, I am playing great tennis."

Draper and Musetti were reuniting for the first time since their maiden top-level meeting at last year's Next Gen ATP Finals, where the Briton sunk his fellow youngster in three sets during the round-robin stage, but a disastrous opener saw the world number 82 lose serve straight away.

Draper squandered two chances to break back straight away as Musetti established a two-game advantage, which was wiped out in the eighth game as the world number 82 found a sixth gear and broke to 15 to level at 4-4.

After coming close to losing serve again in the 11th game, a late surge from Draper saw the Briton bring up two set points, and an undercooked dropshot from Musetti handed his opponent the opener.

It was Musetti's turn to miss two break points early doors in the second set, and Draper capitalised to race into a 3-0 lead before wasting a golden chance to earn the double break in the sixth game.

However, the 21-year-old found himself with two match points on Musetti's next service game, and while the Italian saved one, he proceeded to net a cross-court forehand as Draper set up a last-eight showdown with Turkish qualifier Cem Ilkel.

Draper would have been on course to meet compatriot Billy Harris in the semi-finals, but the world number 221's first-ever ATP Tour main-draw appearance came to a close with a straight-sets loss to German third seed Jan-Lennard Struff.

Harris more than held his own against the world number 28, but Struff came through 7-6[5] 6-4 in one hour and 37 minutes, hitting 11 aces and only suffering one loss of serve throughout the battle.