"She's a good grass-court player and is going really well" Williams added.
The 23-time Grand Slam champion beat out German player, No. 13 seed Julia Goerges, Thursday in a 6-2, 6-4 victory to advance to the women's final.
"It's insane. I don't even know how to feel, you know, because literally, didn't expect to do this well in my fourth tournament back", said Williams who returned to tournament play in March after a 13-month absence. "That's kind of what I'm doing".
That's not the case.
Kerber lost to Serena Williams in the 2016 final and could face a rematch with the seven-time champion, who is due next on Centre Court against 13th-seeded Julia Goerges.
After hitting five aces with a serve that reached 119 miles per hour, delivering 16 winners to only seven unforced errors, and covering the court so well with speed and effort against Goerges, Williams will face another German, 11th-seeded Angelique Kerber, on Saturday. But the American discovered to be human and double faulted as Goerges played her best shots of the match to create her first break point chances.
That enjoyment was clear to see as she dashed Goerges's hopes of setting up an all-German final with Angelique Kerber in 70 unforgiving minutes. Ostapenko, who has a volatile game, finally broke Kerber's serve in the second set, but by that point she was already down 1-5 and it wasn't enough.
After giving birth to daughter Olympia last September, Williams dealt with issues including blood clots, and she's been wearing compression leggings this fortnight as a precaution.
The final tally told the story: Ostapenko had far more winners, 30-10, but also far more unforced errors, 36-7.
Jelena Ostapenko has started her first Wimbledon semifinal. She had 14 winners and 10 unforced errors, while Kerber had three winners and - this was key - zero unforced errors.
There were no drawn-out points in the early going, no lengthy baseline exchanges, essentially because Ostapenko wouldn't allow it. Williams is playing in her fourth tournament and her second Grand Slam since missing more than a year with her pregnancy, but you'd never know it looking at her. She won here I don't know how many times.
Eventually, Kerber's style ruled the day. Ostapenko's strokes were missing and she grew increasingly frustrated, slapping a thigh after a miss or leaning forward and putting her hands on her knees after others.
The first two points played by Ostapenko - who won the French Open in 2017 and crashed out in the first round the following year - were emblematic of the match.