Complex sentence: In the first round of the main draw, Zhang caused a huge upset by defeating world number two Simona Halep in straight sets, her first win in the main draw of a Grand Slam Tournament.
Split into simpler sentences: In the first round of the main draw, Zhang caused a huge upset by defeating world number two Simona Halep in straight sets. This was Shuai's first win in the main draw of a Grand Slam Tournament.