Note: You can find the full order of play for today's matches - as well as live stream links - on our schedule page.
Due to weather delays this morning, certain matches on outer courts have been delayed. Listed times may change.
Here's what to look for on day two of tennis at the Rio Olympics:
The Williams sisters are down a set and a break, 6-3, 3-2. It would be their first Olympic loss as a duo.
Muguruza is up a set and two games.
Spain's Garbine Muguruza will take to Centre Court shortly. She's the 2016 French Open champion who's seeded third in Rio singles.
This is her debut Olympics.
Venus and Serena Williams begin their doubles campaign now.
The Venus/Serena Williams doubles match against the Czech Republic's Lucie Safarova and Barbora Strycova should begin around 5:15 PM ET.
Here are some video highlights from two of today's biggest matches while we wait for Centre Court action.
It may have been drizzling outside, but Rafael Nadal was on fire.
He crushed Argentina's Federico Delbonis, 6-2, 6-1. The Spaniard showed signs of his old self - confident, strong, fast.
Andy Murray handily defeats his first - but potentially, not last - Serbian opponent, Viktor Troicki.
After a slow start, Great Britain's number two seed Andy Murray rips open the first set against Serbia's v. He takes the lead, 6-3.
Meanwhile, Nadal is currently playing on court 1. He and Argentinian opponent Federico Delbonis have each won a game in the first set.
Can't choose between your favorite men's players? Bravo is switching back and forth between the two matches. Or you could open two browsers:
Angelique Kerber, the number two seed who beat Serena Williams in this year's Australian Open final, won her first round match in straight sets. The score was 6-3, 7-5.
Spain's Rafael Nadal - returning to tennis after a three-month wrist injury - is up next on court one.
Serena Williams makes quick work of first round opponent Daria Gavrilova, 6-4, 6-2.
Andy Murray is up next on Centre Court.
Serena Williams takes the first set, 6-4.
Please note that the schedule available on NBCOlympics.com may be a bit off due to this morning's weather delays. The appropriate changes will be made when necessary.
Good news for Venus Williams fans: Though she suffered a tough singles loss last night to Belgium's Kirsten Flipkens, the former World No. 1 will compete in doubles today alongside sister Serena.
That match is scheduled to be the fourth on court 1. Due to weather delays, match 1 on that court is still ongoing.
Play has begun on courts 1, 2, 3 and 4.
Serena Williams takes to Centre Court. Her match should start any moment now.
However, outer court matches have been delayed yet again. NBC Olympics will let you know when those matches are set to resume.
Brown retires due to injury, Bellucci advances into the second round.
Next up on Centre Court: Serena Williams.
Court 1 will not see play before 11:30 ET.
Though he was only five points from victory, Brown misstepped and seemed to suffer a severe ankle injury. He's taken a medical timeout.
Djokovic's opponent tonight, Argentina's Juan Martin del Potro, may hit the ball a bit harder than usual - he's got reason to be angry.
Del Potro got stucked in an elevator in the Olympic Village for nearly 40 minutes. He was finally freed by the Argentine handball team.
Here's a photo from Twitter:
More weather delays. Matches on outer courts will not begin before 11:00 AM ET, and are more likely to start on courts 1 and 2 than courts 3 and 4 due to infrastructure of the facilities.
Excited for Serena Williams' Rio debut this morning? Here's a picture from her Instagram featuring some of Team USA's best female tennis players.
High winds - so intense, they're reportedly shaking the cameras - have delayed play on all outer courts. Currently, only Centre Court is going on as scheduled.
One of today's hottest match-ups: Serbia's World No. 1 Novak Djokovic vs. Argentina's Juan Martin del Potro. Unfortunately, it doesn't start until approximately 8 PM - the last match on Centre Court.
But Djokovic gave fans a sneak peek into his preparations in an image he posted to Instagram.
Good morning. We're about to kick off with Germany's Dustin Brown playing Brazil's Thomas Belluci on Centre Court at 9:45 AM ET. You can find the stream here.
From morning through evening, there will be five courts simultaneously streamed: Centre Court, court 1, court 2, court 3 and court 4. More information is available on the schedule page (above).
Please note: Matches may start earlier or later depending on the preceding matches and/or weather conditions.
NBC Olympics has also written a preview in advance of all of today's matches.