Williams won that one for a second consecutive title at the All England Club, before missing the grass-court tournament previous year while pregnant.
The second set was quite simply a masterclass in precision groundstrokes from Kerber as she again broke early to seize the advantage.
Serena Williams longs to tell her daughter how she bound her longtime label, champion, with her newer one, mother.
The 23-time slam champion will equal Margaret Court's all-time haul of major titles if she beats Kerber on Saturday. To hear people say, "Oh, she's a favourite" - the last 16 months, I've played four tournaments, and was carrying another human half that time.
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 first of the two matches on Centre Court seemed to hold more promise given the contrasting styles of the two players.
'She's trying to, yeah, playing like she played the years before where she won the big matches.
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"[But] Every time I go out there, I want to I guess take a giant step forward, keep taking giant steps, but keep improving".
Williams will now face Angelique Kerber in Saturday's final in a repeat of the 2016 showpiece, a match the American won in straight sets. By the end, Ostapenko had far more winners, 30-10, and far more unforced errors, 36-7. Suddenly, Williams' place in another All England Club final began to seem all but assured - while also feeling like entirely too much to expect so soon.
She was, instead, going to employ spectacular defense and solid, steady play, while letting her opponent, Jelena Ostapenko, be the one to determine the outcomes of almost every point.
Williams, who is chasing her 24th Grand Slam title, returned to tennis in March, but failed to achieve any considerable progress in her first tournaments and struggled to regain decent competitive shape.
It took Kerber two tries to serve out the victory, getting broken to 5-2.
To the crowd's delight, the Latvian came back strongly winning one of the three break points she had in the next game and then holding her own to reduce the margin to 3-5. "For me, I only see joy out of it", Williams said with a smile.