Williams, who was representing her nation in Perth alongside John Isner, began proceedings with a victory over Flavia Pennetta.
The World No. 1, however, was not her usual self in the opening stages as she lost the first set of the match to love -- a "bagel" -- leading her to request an espresso to help blow away the cobwebs.
The hot drink seemed to do the trick, as Williams went on to dominate Pennetta, dropping just three more games and going on to win 0-6 6-3 6-0.
The 33-year-old finished up with five aces and 31 winners to help make up for the 38 unforced errors in her first match of the new season.
"I wanted coffee with my bagel and whatever coffee it was, it was really good," Williams said in an on-court interview afterwards.
"I'm so jet lagged and Flavia played really, really well. And yeah, everyone needs coffee every now and then. I needed coffee to get my feet moving."
Williams had asked a ball girl to get her the espresso, though she was unsure as to whether she would even be allowed to drink it.
"I just asked them to get me a shot of espresso. I asked them if it was legal, because I've never done it before," she added to reporters.
"I am a coffee drinker. I didn't have mine this morning and I was just feeling it, so I just had to get some coffee into me."
After Williams had set U.S. on their way, Isner secured the win over Italy by defeating Fabio Fognini 7-5 5-7 7-6 (7-4).
The World No.18 needed his big serve to help see him through, with the 29-year-old serving 18 aces and just one double fault, while he also hit 47 winners on route to victory.
Williams and Isner then joined forces in the mixed doubles to complete the whitewash by defeating Pennetta and Fognini 6-2 2-6 11-9.
United States next take on Canada in Group A Tuesday, with Eugenie Bouchard and Vasek Pospisil looking to recover from their 2-1 loss to Czech Republic Sunday.