The 17th-seeded Rybakina dropped her first set of the grass-court tournament overnight but broke her Australian opponent early in the second and third sets.
Rybakina hit 15 aces against Tomljanovic on court one and will next face 2019 Wimbledon champion Simona Halep for a spot in the final.
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It was a bitter ending to an excellent tournament from Tomljanovic, who admitted she missed an opportunity against Rybakina.
“I came in (today) really believing that I could win, where maybe that wasn’t the case last year. That’s what’s just extra disappointing,” she said.
“It was a bit disappointing because I felt like I played a really good first set. (It was) actually one of the cleanest sets I’ve played all tournament.
“I felt like the middle of that second she definitely raised her level. I mean, she started serving really, really good. And just less errors from the back.
“I tried to fight my way back. It was too far gone. I mean, that 3-5 game, again, she served crazy good. Yeah (I’m) just disappointed because I felt like with my game I was really there.”