After beating the top seeds on Wednesday, Sitak and Sharan had high hopes going into this encounter.
The first set was tight. Games went with serve, with neither team particularly troubled, until Vliergen got the wobbles serving at 5-6.
Sharan missed an easy backhand at 30-30, but the New Zealand-Indian combination took the next rally, to force the first break-point of the match, as doubles no longer have deuce points.
It was converted, to Sitak's obvious delight, thanks to his swift intercept at the net for a forehand winner.
But the Belgian duo, who won titles at Bastad, Gstaad and Zhuhai last year, found their groove in the second set.
First Sharan was broken, then Sitak, with the New Zealander double faulting to give the Europeans a 4-1 lead. Sitak and Sharan retrieved one break, and then got lucky with a net cord to level at 5-5.
They had two match points in the next game, but the Belgian held strong, which ensured a tiebreak.
The Belgian seemed to gain momentum from their lifeline, taking the breaker 7-3, after getting an early advantage.
The super tiebreaker was tense, though the Europeans always looked more assertive. Sitak saved one match point at 8-9, but Sharan dumped a volley into the net on the next to end the contest.