Dan Evans beat Bernard Tomic to progress through to the second round of the Intrum Stockholm Open.
Eighth seed Evans celebrated becoming the British number one on Monday by securing victory in three sets, prevailing 6-4 1-6 6-3.
Australian Tomic fought back after going a set down, winning the second set comfortably in 33 minutes to take the match to a decisive set.
In the end the world number 43 from Great Britain proved too good, with Tomic saving two match points before Evans saw out the contest in an hour and 54 minutes.
Evans is set to face Norway's Casper Ruud or Serb Filip Krajinovic in the second round, with third seed Taylor Fritz a potential quarter-final opponent.
American and sixth tournament seed Reilly Opelka fell to Italian Stefano Travaglia 7-5 4-6 6-4.
In Antwerp at the European Open, former world number five Jo-Wilfried Tsonga beat Lorenzo Sonego in straight sets.
Fifth seed Guido Pella needed three sets to beat Peter Gojowczyk, going through 5-7 6-4 7-6 (2) against the world number 111.