Fresh off a thrilling third-round battle with Emma Raducanu, reigning champion Sabalenka had an easier ride against the Spaniard, earning her tour-leading 50th win in 80 minutes.
"I was up a break, made a couple of mistakes and she broke me back," Sabalenka said.
"I'm glad to win in straight sets. I didn't want to stay for three hours."
The Belarusian will next meet Elena Rybakina in a final-worthy showdown, as the ninth-seeded Kazakh rallied to beat American Madison Keys 6-7 (3-7) 6-4 6-2.
Earlier, third seed Iga Swiatek reached the quarters with a 6-4 6-4 win over Sorana Cirstea.
The Wimbledon champion extended her perfect record against the Romanian to 5-0 and will next face Anna Kalinskaya after she won the all-Russian clash against Ekaterina Alexandrova, 3-6 7-6 (7-5) 6-1.
"We played many tough matches, so I know Sorana can really hit the ball well, especially on faster surfaces," former world No.1 and six-time grand slam champion Swiatek said after her 95-minute triumph.
"I'm happy I was solid enough. I was trying to be proactive with my serve, not many of my first serves went in, but I was happy I was solid on my second serves."
Cincinnati is one of only three WTA 1000 events on the current calendar that Swiatek has played without yet reaching the final. She was a semi-finalist there in both of the past two years, falling to Coco Gauff in 2023 and Sabalenka last year.
Swiatek's fellow Pole Magda Linette upset fourth seed Jessica Pegula 7-6 (7-5) 3-6 6-3 in a third-round match that extended over two days after Tuesday's suspension due to rain.
The American had levelled the match at a set apiece, but on Wednesday's resumption Linette earned the break before closing it out on serve for her second Top-10 win of the season.
Veronika Kudermetova will face Linette is the next round after the Russian's 3-6 7-6 (7-4) 6-4 success against 16th-seeded Dane Clara Tauson.
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