Sonego, whose semi-final against Pablo Carreno Busta was suspended due to rain on Friday, returned to the court on Saturday morning to defeat the Spaniard before surviving an early onslaught by the 19-year-old Kecmanovic.
The teenager showed plenty of grit throughout the contest saving seven of the nine break points he faced, but served poorly, landing just 56% of his first serves, while Sonego grew stronger as the match progressed.
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The 24-year-old Italian sent down 25 aces to Kecmanovic's five and won 85% of his first serve points as he wrapped up the win in a little under three hours.
Sonego kicks off his Wimbledon campaign against Spanish qualifier Marcel Granollers, while Kecmanovic faces another Spaniard, Roberto Carballes Baena, in his opening match at the All England Club.
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