Sofia (Bulgaria), Sep 29 (IANS): Danish tennis player Holger Rune showed his fighting qualities at the Sofia Open on Thursday, earning a comeback win against Lorenzo Sonego to reach his sixth tour-level quarterfinal of the season.

In a hard-fought clash, the 19-year-old rallied past the Italian 6-7(1), 6-4, 6-3 in two hours and 19 minutes at the ATP 250 hard-court event.

"I feel very good. Today was a tough match...Lorenzo won a title last week, so he had a lot of confidence. I took my chances, played well and stayed in the moment, so I am proud," Rune said in his on-court interview.

The fifth seed struck 38 winners and won 85 percent (44/52) of his first-serve points against Sonego, who won his third tour-level title in Metz last week. Rune will continue his quest for a second tour-level title when plays Ilya Ivashka in the last eight.

The Dane is fourth in the ATP Live Race To Milan as he looks to qualify for the Intesa Sanpaolo Next Gen ATP Finals for a second consecutive year. Rune has enjoyed a breakthrough season, highlighted by his maiden tour-level trophy in Munich in May.

Meanwhile, German qualifier Jan-Lennard Struff also booked his spot in the last eight, dispatching French qualifier Ugo Humbert 6-3, 6-1. Struff, who is making his third appearance in Sofia, will next play Lorenzo Musetti as he seeks to reach his first tour-level semifinal of the season.

Pole Kamil Majchrzak upset eighth seed Oscar Otte 4-6, 6-2, 6-4 to advance to his third tour-level quarterfinal of the year.

The 26-year-old will next take on Marc-Andrea Huesler after the Swiss upset World No 14 Pablo Carreno Busta 6-3, 3-6, 6-2 to earn his first Top 20 win of the season. The World No 95 broke Carreno Busta three times to advance after one hour and 44 minutes.