It's certainly an interesting duo: One is trying to recover from, by her standards, a disappointing 2014 so far (Serena); and the other continues her comeback from a foot injury, back on her favorite surface.
Most of the attention, however, will be on Williams.
She's the first of five players to particularly keep an eye on during the US Open Series.
The answer isn't known.
But what we do know is that it's the first time in a season since 2001 that Williams hasn't reached a Grand Slam final when she's contested the first three majors of a campaign.
And that was when Williams was merely 19.
Now approaching her 33rd birthday, the pressure is sure to rise on Williams during the US Open Series and especially in New York.
Observers are rightly asking if Williams has lost her killer instinct - if Williams herself has any self-doubt, landing that 18th Grand Slam title (to tie Chrissy and Martina) will become problematic.
After a vacation in Croatia, claiming a third title in Stanford - and in emphatic fashion - would be the start Williams wants and perhaps, needs.
Petra Kvitova: When Li Na won her second Grand Slam title in Melbourne this year, the thinking went (or at least from this author) that she could relax and thus become even more of a threat. After all, Li can play on all surfaces.
Will it be different for the younger Kvitova?
Yes, Kvitova has admitted that the humidity in North America adversely impacts her asthma, but don't forget that in 2012, the Czech won in Montréal, reached the semifinals in Cincinnati and won in New Haven.
Eugenie Bouchard: Montréal is a hockey town, boasting arguably the most storied NHL franchise in the world in the Montréal Canadiens. But there won't be many more prized tickets this year than when Bouchard takes to the court in her hometown in a week-and-a-half.
Bouchard acquitted herself just fine in her last tournament on home soil last year, making the semifinals in Québec City, and she's already one of tennis' best competitors.
Some players thrive at home and others crumble; Bouchard seems to fall in the first category.
As someone who has always said that she feels she belongs with the elite in tennis, we wouldn't expect Bouchard to have a letdown this summer.
She craves much more success.
Simona Halep: Unless she makes a last-minute alteration, a repeat of the Wimbledon semifinal between Bouchard and Halep - the first set was one of the best of the tournament - in Montréal is out of the question since the Romanian isn't scheduled to compete in Canada.
But don't think that Halep, a workhorse - a talented one, at that - is slowing down. She, of course, didn't take a break immediately after Wimbledon, competing at home in Bucharest, and beat Roberta Vinci in the final to move 11 points behind Maria Sharapova atop the Road To Singapore leaderboard.
But will fatigue, at some point, catch up to both Halep and Bouchard?
Of those in the top 10 in the race to Singapore, Bouchard has played the most tournaments, tied with Angelique Kerber at 15. Halep follows at 14.
Agnieszka Radwanska: This is a big next couple of months for Radwanska.
For so long, things were going smoothly for the perennial fan favorite and 2012 Wimbledon finalist from Poland.
Makarova has been known to thrive on grass, but the 6-3, 6-0 score left many doing a double take.
Is it the start of a slide in the rankings for a player who might have overachieved in the last couple of years or a minor blip that will be rectified on probably her preferred surface?
Radwanska and Ivanovic, with her new coach, are in the field in Stanford, too.