Having shaken off any rust that may have remained from her absence, Williams appears to be closing in on top form at the right time.
Ostapenko, the 12th seed, overpowered Slovak Dominika Cibulkova 7-5 6-4 to reach Wimbledon's final four for the first time, and without dropping a set.
The 36-year-old will play German 13th seed Julia Goerges on Thursday for a place in Saturday's final boasting a 3-0 career record. "After the first set, I just said, 'Let's go three sets.' I just kept fighting".
"I don't follow tennis", the Italian said when the subject of Williams' return came up before today's quarter-final.
Suddenly, Williams looks as great as the eight Wimbledon titles suggest she is.
Ostapenko also reached the quarterfinals previous year in her best Wimbledon showing, losing to eventual runner-up Venus Williams.
"It's definitely family before tennis for me", she said to Harper's Bazaar UK.
Both two-time Grand Slam champion Kerber and 21-year-old Kasatkina reached the quarterfinals at last month's French Open.
Even when Serena was on the brink of losing the set, she managed to hit a 122 miles per hour serve, her fastest of the tournament. An unusual forehand error at 15-30 made the difference for Williams as Giorgi broke to move 4-2 up.
Rebounding from her shock first-round elimination in her Roland Garros title defence, Ostapenko has marched through the Wimbledon draw without dropping a set.
"It was a very tough match but I was just trying to enjoy it".
"It's pretty unreal for me", said Goerges, who reached her first major semifinal at a tournament where she exited in the first round each of the past five years. The two met last month in the second round at the French Open, with Williams winning in straight sets. It also means she now has 90 Wimbledon wins, the most amongst active female players and she has not dropped a set yet in this tournament. "Everybody has the same chances to win that match, and I'm looking forward to it".
That put Giorgi 5-2 ahead, owing to her earlier break of serve, and gave her the impetus to win the set - the first that Williams had lost in this tournament.
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