From Big 3 masks to Giorgi's handshake, the first day of the US Open did not disappoint. (AP) 

The first day of the US Open went as expected. Serena Williams extended her winning streak over Maria Sharapova. Novak Djokovic won his opener in straight sets. And Roger Federer was challenged early, but came away with a convincing victory. 

But that doesn't mean the day was without excitement. Here are five weird and wonderful moments that went under the radar on Day 1:

1

"I am the BEST"

The past three seasons have been glorious for fans of Federer, Djokovic and Rafael Nadal. The three have won every single Grand Slam, and they've pushed one another to mind-boggling career-major tallies. US Open patrons are renowned for their passion, but this group in masks took it to a creepy level: 

2

Who are you wearing? 

No. 29 seed Hsieh Su-Wei, who recently won the Wimbledon doubles championship, brings her own sense of style to every tournament she plays. But she stood out even more than usual on Monday, when she wore a US Open-themed kit. It would look as though she just bought it at the National Tennis Center, except the logo on her dress and visor has been out of use for years. 

3

"Bye-bye!" 

You don't have to be a great English speaker to give a great post-match speech, Juan Ignacio Londero proved on Grandstand. Being interviewed after his win over Sam Querrey, Londero answered: "My English is so bad. All people understand. I'm happy for the match today. Congrats for Sam. And see you tomorrow, sorry. Bye-bye!" 

The crowd, in the words of host Blair Henley, went wild. 

4

"Popalopabenkowicz"

Anastasia Pavlyuchenkova recently started working with Canadian coach Rob Steckley, who specializes on the side in making off-the-wall videos with his players. Pavlyuchenkova had already released this gem in the lead-in to the tournament ... 

And on Monday came the follow-up: 

5

#ImJustHereForTheHandshake​

Camila Giorgi was one of several blowout victims on Monday, going out, 6-1, 6-0, to Maria Sakkari. And when it was over, she left the court quickly and dramatically:

It's one day down and 13 to go in Flushing Meadows, so there'll be plenty more smiles, laughs and drama before the year's last Slam champions are crowned.