Stan Wawrinka and Roger Federer will go head to head later on Friday after the latter overcame Leonardo Mayer in straight sets.
Grigor Dimitrov's Cincinnati Masters defence was brought to an end by Novak Djokovic in a match held over from Friday.
Lesia Tsurenko will take on Simona Halep later on Friday after the French Open champion beat Ashleigh Barty in the third round.
Madison Keys lost the opening set but hit 55 winners to upstage Wimbledon champion and fourth seed Angelique Kerber on Thursday.
Rain wreaked havoc again as only three matches were completed at the ATP Masters 1000 tournament on Thursday.
Prior to her 6-1 6-0 defeat to Johanna Konta in San Jose, Serena Williams discovered some shocking and emotional news.
After transformations to the Davis Cup were voted through on Thursday, Tennis Australia said it was "extremely disappointed".
The International Tennis Federation's proposals for a new Davis Cup format were passed by a vote in Orlando on Thursday.
While Novak Djokovic and Grigor Dimitrov won in Cincinnati on Wednesday, Alexander Zverev said goodbye.
Simona Halep was leading 4-3 and 30-15 in the final set against Alja Tomljanovic when rain washed out play on Wednesday.
Kyle Edmund earned his first Cincinnati victory by defeating Mackenzie McDonald 6-3 6-2 on Sunday.
Nick Kyrgios was left standing on court in his socks before a match at the Cincinnati Masters on Ohio, where Roger Federer won convincingly.
Novak Djokovic and Roger Federer will meet for a 46th time in the Cincinnati Masters final and the Swiss is unsure how it will play out.
Having not played since his Wimbledon quarter-final exit, Roger Federer made a winning comeback on Tuesday.
Following her defeat to Petra Kvitova at the Cincinnati Masters, Serena Williams struck an optimistic tone.
A candid Serena Williams discussed the difficulties of juggling professional tennis and motherhood after her win at the Cincinnati Masters.
Novak Djokovic was seen by medical staff at the Cincinnati Masters but then reeled off six successive games in beating Adrian Mannarino.
Serena Williams was back on form at the Cincinnati Masters, but she came off second best in a titanic tussle with Petra Kvitova.
Sloane Stephens has pushed Simona Halep all the way in two finals in 2018 and the Romanian believes it has made her a better player.