The Rio Olympics may have started on Saturday, but Sunday they announced their presence with authority.

Day 2 provided the most exciting moments of the games thus far, highlighted by U.S. swimmers and gymnasts dominating their events. Team USA put the rest of the world on notice with outstanding performances in the pool and at the gym.

Here are some takeaways from Day 2's swimming finals and women's gymnastics qualifying.

Phelps comes through

There was some debate as to whether Michael Phelps should have even been included in the men's 4x100-meter freestyle relay, and boy did he prove his doubters wrong. Phelps swam an incredible 100-meter in the second leg to give the U.S. a lead it would never relinquish. Nathan Adrian closed out the race to edge France and Australia for the gold.

Ledecky bests herself

Katie Ledecky's biggest competition during the 400m freestyle final was, well, Katie Ledecky. But even she wasn't that much competition, as she smashed her previous world record, beating the closest competitor by nearly five seconds. Ledecky won silver in the 4x100m freestyle relay on Saturday, and hopes to win gold in three more events.

USA gymnasts are really, really good

The American women's gymnastics team put up the highest score in every discipline en route to the top qualifying score. Individually, Simone Biles qualified with the top score -- as expected -- and Aly Raisman took the second American spot, meaning Gabby Douglas will not defend her 2012 gold. The U.S. is going to take home a lot of gold over the next few days.

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