Partner Tiafoe lost his service for the Americans to lose the opening set and she also appeared to be nursing a right shoulder injury although she insisted it was of no concern with the Australian Open looming.
Earlier, Federer hardly broke sweat in his singles match against Tiafoe, taking his game up a notch at 4-4 in the first set to win 6-4 6-1.
The 23-time grand slam victor wasn't particularly hindered by the inconvenience however, snaring two breaks in the second set to wrap up the match in 104 minutes.
Williams, who lost to her sister Venus in an exhibition match in Abu Dhabi last week, will be back in action on Tuesday night when the United States take on the Roger Federer-led Switzerland. I would even cry sometimes just because....
Serena: 'It was a great experience. "This is super cool that we get to do it at such a pinnacle point of our careers", Williams said.
"This guy (Federer) is great, both off the court and on the court". He's the greatest of all time. There's a reason he's the greatest. "You just can't read it".
The pair had mutual appreciation for each other, particularly when it came to their serves.
Both Federer and Williams say they're excited about the historic matchup.
"I've played with some of the greatest doubles players in the world in Martina Navratilova and Martina Hingis, and I've also played against some of the best in Venus and other great ones in the past.
What an honour", said Federer.
After much anticipation, the first set in the mixed rubber was a little disappointing, with neither Federer nor Serena returning any of the other's serves. "It's been a while since I've been there", she said. "I hope that a lot of tennis fans are going to tune in and watch it, because it's going to be one time and probably never again, in this kind of a competition".
Playing in front of the highest single session attendance in the tournament's history, the team of Federer and Belinda Bencic beat Williams and Frances Tiafoe 4-2 4-3 (3) to clinch the tie to top the group.
The much-celebrated mixed-doubles contest secured a 2-1 win for Switzerland in the round-robin tie.
Defending champion Switzerland will qualify for Saturday's final if it beats Greece on Thursday.
Donald Trump has 5 more days to spin his border wall story into a spaghetti bowl of cultural and racial falsehoods. Some federal workers began to feel the pain of the partial USA government shutdown on Friday.
The 5-1 win at the Cardiff City Stadium was the first time United have scored five in a Premier League match since Sir Alex Ferguson's last game in charge more than five years ago. "I don't think he (Solskjaer) has stopped smiling", Young said.
The only public offer comes from the hedge fund controlled by Sears chairman Eddie Lampert, though it's not yet an official bid. The company released a list of the closing Sears and Kmart locations online and released the following statement.
But he added: 'Eden is better when he comes to play with the midfielders, it's better to open spaces for the wingers'. Eden Hazard has suggested that he will not consider extending his contract at Chelsea FC until the end of the season.
Workers are not paid in full while on leave, though are customarily compensated with backdated pay once the shutdown is over. State highway workers were sent to the area Monday to erect "no parking" signs along US 70 outside the monument.
It looks like Christmas will be over and done with before the federal government will have a chance to get fully back to business. Asked whether he's willing to increase the price tag as long as the money is not spent on a wall, Durbin responded: "Absolutely".
Mayweather , who has won all 50 of his professional fights, insisted he was "still retired" after the exhibition . As for Nasukawa, he remains 28-0 in kickboxing and 4-0 in MMA, seemingly with a bright future ahead of him.
Advancing issues outnumbered declining ones on the NYSE by a 4.84-to-1 ratio; on Nasdaq, a 3.80-to-1 ratio favoured advancers. The Nasdaq was up 4 percent and on track to wipe out Monday's losses. the S&P posted a 2.9 percent pop in afternoon trading.
The former " Suits " star could be seen placing a protective hand on Kate's back as the pair made their way inside the gates. Last year, she became the first non-married partner to be invited to Christmas lunch at Sandringham with the Queen.
China allows first-ever US rice imports ahead of trade talks
The two sides have been participating in phone meetings and will continue to do so in an "intensive" manner, according to Reuters. Beijing recently announced a third round of tariff cuts, lowering the duties on more than 700 goods starting January first.
Bright light mystifies New Yorkers after transformer fire
The scattered power outage has also interrupted traffic at LaGuardia Airport , with only certain flights allowed to depart. Some began looking for a scientific explanation as to why a power plant failure would produce blue light specifically.
Miley Cyrus and Liam Hemsworth are officially married
On Wednesday, she finally confirmed that they'd tied the knot and uploaded the glorious wedding images we were all waiting for. Cyrus and Hemsworth's private wedding comes after a rocky, on-again , off-again relationship between the Last Song costars.
Major Storm Whipping Up Blizzard Conditions
In a special weather statement, Environment Canada said "a significant winter storm is expected Thursday night into Friday night". As of right now, it looks like we'll start off the new year with some of the coldest temperatures of the winter season thus far.
Donald Trump asks boy, 7, if he still believes in Santa
Santa does not want to rush the important job of delivering presents to children and spreading Christmas joy around the world. There's also a selection of "Santa Cam" videos , which document such things as his initial spotting at the North Pole.
US Supreme Court rejects Trump request to enforce asylum ban
How did the justices vote? New Justice Brett Kavanaugh and three other conservative justices sided with the administration. The administration had also complained that the nationwide order preventing the policy from taking effect was too broad.