World No.1 Serena Williams called for a coffee to perk her up during a 0-6 6-3 6-0 win over Italian Flavia Pennetta at the Hopman Cup on Monday.

Williams, who only arrived in Perth on Saturday, was flat early in her match and, at 5-0 down in the first set, called on a ball girl to fetch her an espresso.

The 33-year-old had her caffeine fix after losing the first set in just 19 minutes, and she finally started to find her groove in the second set.

And once Pennetta’s serving game capitulated, Williams dominated to win the match in 89 minutes.

“It’s miracle coffee,” Williams joked after the match.

“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.

“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.

“But I needed to wake up – it’s just the jetlag. It gets you all the time.”

Williams said the round-robin nature of the Hopman Cup meant she didn’t need to stress as much, and her goal this year is to enjoy herself more on court.

“I’ve never smiled so much in a match before,” Williams said.

“This year my whole goal is to have fun.

“My dad says, ‘Serena, you’ve done everything, enjoy yourself, I promise you’ll play better’.

“So I’m like, ‘Ok’. I’m trying to relax a bit more and play how I know I can play.”

Big-serving world No.18 John Isner can secure the tie for the US with victory over Fabio Fognini in the men’s singles rubber.

The mercury was already above 34 degrees when Williams’ match started at 10am local time.

But with the Perth Arena roof closed, the cool conditions should have ensured a high-octane match.

Instead, Williams’ lethargy paved the way for a first-set romp, before the 18-time grand slam singles champion finally found her energy and fighting spirit.