Sonmez, who has enjoyed a strong 2026 so far, reaching the Australian third round and becoming the first Turkish woman in the Open Era to win a match there, is currently sitting at a career-high ranking of 67, and showed her vast improvement against the Spaniard.
There were seven breaks of serve in a topsy-turvy first set, before Sonmez saved three set points at 4-5, 0-40 to eventually take the opener. She had a far more straightforward time in the second set, sealing the win in an hour and 53 minutes.
Elena Gabriela Ruse, who reached the first WTA 500 semi-final of her career just under two weeks ago in Linz, had to dig deep to see off Antonia Ruzic, 6-3, 4-6, 6-0.
However, there was no such luck for Eva Lys, who fell to a 6-4, 6-3 loss to Shuai Zhang. The German has struggled to find her best form after picking up an injury at the Australian Open, with Zhang ending a six-match losing streak.
Over on the men's side of the tournament, 2014 US Open champion Marin Cilic secured a fine win over Zizou Bergs, coming from a set down to triumph 4-6, 6-3, 6-4.
The 37-year-old will now face Joao Fonseca in the second round - a player 18 years his junior.