Note: You can find the full order of play for today's matches - as well as live stream links - on our schedule page.
Here's what to look for on day two of tennis at the Rio Olympics:
American World No. 1 Serena Williams is about to take to Centre Court, playing France's doubles specialist Alize Cornet.
American duo Jack Sock and Steve Johnson win their second round doubles match.
On court 2, 3rd-seeded Garbine Muguruza of Spain takes the first set off of Japan's Nao Hibino.
In an upset, France's 5th-seeded Jo-Wilfried Tsonga loses to Luxembourg's Gilles Muller 6-4, 6-3.
Here are some Keys highlights just ahead of Serena Williams' second round Centre Court match at 5:45 PM ET.
Del Potro finally clinches his match against Sousa, winning 6-3 in the third set.
The American men's duo of Jack Sock and Steve Johnson are now up a set in their second round doubles match.
The del Potro match is heating up, with the Argentine and his Portugese opponent tied a set a piece.
On the doubles front, American men Johnson and Sock now play Columbian team Nestor and Daniel.
Juan Martin del Potro is up a set on Sousa.
Last night's surprise winner, Argentina's unseeded Juan Martin del Potro, plays Portugal's Joao Sousa on Centre Court now.
Keys barely escapes, winning 7-5, 6(4)-7(7), 7(7)-6(5).
After trading sets, the U.S.' number 7 seed Madison Keys and France's unseeded Kristina Mladenovic are headed for a third-set tiebreak.
Germany's Angelique Kerber wins against Canada's Eugenie Bouchard, 6-4, 6-2.
Here's video from the London 2012 Olympic Games, where Argentina's Juan Martin del Potro defeated Serbia's Novak Djokovic in singles for the first time.
Kerber takes the first set, 6-4.
After winning a second set tiebreak 7(7)-6(4), the Keys-Mladenovic match is going to a third set.
Kerber/Bouchard is tied 4-4 in the first set.
Today's big updates so far:
Missed all the craziness from last night? Here are some video recaps.
Play has started on Centre Court and all outer courts.
Be sure to check out the U.S. Madison Keys on court 1 as she takes on France's Kristina Mladenovic.