Teenage lucky loser Andrey Rublev upset Paolo Lorenzi in the Croatia Open final to claim his first ATP World Tour title on Monday (AEST).

Rublev lost in the final qualifying round in Umag, but was handed a spot in the main draw when Borna Coric was forced to withdraw from the clay-court event in his homeland. 

The 19-year-old took full advantage of his opportunity by taking on all comers and sealed an unexpected maiden triumph with a 6-4 6-2 victory over No.4 seed Lorenzi.

World No.74 Rublev was clearly not affected by nerves as he broke Lorenzi twice to open up a 4-1 lead and saw out the set in composed fashion after failing to hold in the sixth game.

Rublev won four games in a row in the second set to defeat the 34-ranked Lorenzi and continue his rise, having reached the last eight on the grass in Halle last month.

The surprise package had also seen off Fabio Fognini and Ivan Dodig to reach his maiden ATP World Tour final.