Naomi Osaka benefitted from the second round defeat of former number one Ashleigh Barty and the failure of Karolina Pliskova to reach the semis in Toronto.
Bianca Andreescu, 19, was up 3-1 with a break of serve when 23-time Grand Slam champion Serena Williams decided she couldn't continue.
Serena Williams, seeded eighth in a tournament she has won three times, will take on home hope Bianca Andreescu in the championship match.
Serena Williams fired 12 aces and didn't face a break point as she beat Naomi Osaka for the first time in three meetings.
It would be the first match between Naomi Osaka and Serena Williams since the Japanese star defeated her childhood idol 6-2, 6-4 in last year's US Open final.
Serena Williams defeated 20th-ranked Elise Mertens of Belgium 6-3, 6-3 at the WTA Toronto tournament.
Indian badminton star PV Sindhu and Thai golfer Ariya Jutanugarn were the other non-tennis players in the top 15.
Despite winning the Wimbledon 2019, Simona Halep is still behind Ashleigh Barty, Naomi Osaka and Karolina Pliskova in the WTA rankings.
Alison Riske tied the knot with her long-time partner Stephen Amritraj, who is the son of former Indian Davis Cup player and captain Anand Amritraj.
Simona Halep lifted Wimbledon title by defeating Serena Williams 6-2,6-2 in straight sets.
The 56-minute dissection of the Serena Williams playbook was the 23-time Slam winner's most lopsided loss in a major final.
Simona Halep captured her second career major with a 6-2, 6-2 victory, adding a maiden Wimbledon to her 2018 Roland Garros triumph.
Simona Halep captured her second career major with a 6-2, 6-2 victory adding a Wimbledon to her 2018 Roland Garros triumph.
Wimbledon 2019 Highlights: Serena Williams vs Simona Halep Tennis Score: Simona Halep thrashed Serena Williams to win her maiden Wimbledon crown.
Simona Halep will face seven-time champion Serena Williams for the title on Saturday.
Serena Williams had to draw on all her strength to get past unseeded compatriot Alison Riske in the last eight.
In the days following her loss to Naomi Osaka in the 2018 U.S. Open final, Serena Williams had trouble falling asleep at her Florida home.
Serena Williams came under enormous pressure from Alison Riske before prevailing in an engrossing contest, 6-4, 4-6, 6-3 in just over two hours.