HUA HIN, Thailand - Monica Niculescu scored a first-round upset at the Toyota Thailand Open presented by E@ on Monday, taking out No.3 seed Hsieh Su-wei in straight sets, 6-4, 7-6(2).

In the first career meeting of two of the most eclectic players on tour, it was the 31-year-old Romanian who served at a 75 percent clip for the match to upset the 33-year-old World No.31 and move into the second round to face Poland's Magda Linette, after she defeated Australian qualifier Priscilla Hon, 6-1, 2-6, 6-2.

"I'm happy that I could play this kind of game. I knew Su-wei is going to be very good...and I knew she's a very interesting opponent, mixing the game, like me," Niculescu said after the match.

"I had to run a lot, fight a lot and mix it up, and I think I did that. I'm happy that I could finish in two, because in the end I was losing a little bit of energy, so I'm happy that I could finish it in the tiebreak."

In a match full of break point opportunities for both players, Niculescu saved 10 of the 15 chances Hsieh held overall, as the first six games of the match saw the players trade breaks. 

Niculescu steadied down the stretch of the opener, as she saved four break points in the eighth game to even the set at 4-4, before breaking serve once more in a similarly-paced game en route to moving ahead by a set.

The two wily veterans traded breaks to begin the second set and to end it, as Hsieh kept the match alive as Niculescu served for the second round to force a tiebreak, but the Romanian built an unassailable 6-0 lead in the tiebreak before she converted her third match point. 

No.6 seed Ajla Tomljanovic and No.8 seed Dayana Yastremska had no such hurdles in the opening round, as each moved past their first foes in straight sets.

Tomljanovic down Switzerland's Stefanie Voegele, 6-1, 7-6(6), as she twice came from a break down and saved two set points in the second set, while Yastremska surrendered just three games in defeating Dutchwoman Arantxa Rus, 6-0, 6-3. 

Wildcard Peng Shuai, alongside Irina-Camelia Begu, Kateryna Kozlova and Mona Barthel also moved through to the second round on Monday, defeating qualifier Chloe Paquet, Evgeniya Rodina, qualifier Conny Perrin, and Fiona Ferro, respectively.