Former world number one Martina Hingis lost 6-4 6-0 to Agnieszka Radwanska in the Fed Cup as she returned to singles tennis after an eight-year absence.
The 34-year-old Swiss twice fought back from a break down in the first set before losing it.
Polish world number nine Radwanska, 26, then dominated a 28-minute second set.
Her sister, Ursula, lost 6-2 6-1 to Timea Bacsinszky to make the score 1-1 between Poland and Switzerland in the World Group play-off.
Hingis, a five-time Grand Slam singles champion, was expected to play only doubles in her first Fed Cup tie for 17 years.
"I'm proud of my performance and looking forward to tomorrow," she said.
"I feel like I definitely have the game to hold on with the best in the world, especially Radwanska. She's not a power player, hitting bombs right and left.
"I felt like I was right there, but that's what makes her a top 10 player - she doesn't give you a point for free and sometimes you wish you didn't have to fight for every single point. That made the difference in the first set."
The Swiss initially retired in 2003, aged 22, because of injuries. She returned in 2005 but retired again in 2007, which coincided with a two-year suspension for a positive drugs test.
Hingis, whose appearance makes her eligible for the 2016 Olympic Games in Rio, is scheduled to play Ursula Radwanska in the fourth rubber on Sunday before partnering Bacsinszky in the concluding doubles match.
In another World Group play-off match, Serena Williams defeated Camila Giorgi 7-6 (7-5) 6-2 to give USA the lead over Italy, before Sara Errani levelled the tie with a 6-1 6-2 victory over Lauren Davis.
Canada's world number seven Eugenie Bouchard suffered a surprise 6-4 6-4 defeat by world number 69 Alexandra Dulgheru of Romania, leaving the tie at 1-1 after day one in Montreal.
Bouchard, last year's Wimbledon finalist, had refused to shake Dulgheru's hand in the pre-match ceremony, saying: "It's nothing personal towards her, I just don't believe in wishing my opponent good luck before the match."
In the World Group semi-finals, Czech Republic lead France 2-0 after wins for Lucie Safarova and Petra Kvitova.
Russia lead Germany by the same margin following victories for Svetlana Kuznetsova and Anastasia Pavluchenkova.