Day 1 of the first-ever ATP Cup did not disappoint with packed action in Brisbane, Perth and Sydney. Here are the Top 5 Photos from January 3. (All photos by Getty Images)

1

In Sydney, Grigor Dimitrov celebrated after he and Alexandar Lazarov upset Great Britain's Jamie Murray and Joe Salisbury, 11-9 in the deciding tiebreaker, to secure a 2-1 win for Bulgaria. 

2

In Brisbane, Alex De Minaur came back from a set down to take out Alexander Zverev and clinch Australia's eventual 3-0 win over Germany. 

3

Nick Kyrgios won the first singles match of the day over Jan-Lennard Struff, and got to cheer his teammate De Minaur to victory. 

4

Also in Brisbane, Denis Shapovalov gave Canada an insurmountable 2-0 lead over Greece by beating Stefanos Tsitsipas in two tiebreak sets. 

5

In Perth, Fabio Fognini couldn't close out a win over Daniil Medvedev despite handily winning the first set, and Italy would lose to the Russians, 3-0.