Fritz gives United States strong start at inaugural United Cup
The mixed team tournament features 18 countries playing in Sydney, Brisbane and Perth, with each tie consisting of two men's and two women's singles rubbers along with a mixed doubles match as players warm up to the Australian Open.
Fritz got his country away to a flying start with a 6-3, 6-4 win over world number 74 Jiri Lehecka at Sydney's Ken Rosewall Arena before Keys saw off Marie Bouzkova 6-4, 6-3.
The 25-year-old Fritz had a breakthrough year in 2022, beating 22-time Grand Slam champion Rafael Nadal in the final at Indian Wells to go with titles in Tokyo and Eastbourne.
He broke into the top 10 in 2022, reaching a career-high eight in October.
Fritz had too much firepower for Lehecka, facing only two break points on his way to a comfortable 75-minute win.
The American admitted he had felt some nerves before the match.
"It was the first match of the season and also playing a team event as well adds to it (the nerves)," he said.
"I think in the beginning of the match I handled it much better than maybe my opponent did. I got the early break, then kind of just held on to it."
Keys, who made the Australian Open semi-finals this year, came back from an early break of serve in both sets to see off Bouzkova in 80 minutes.
The former US Open finalist overpowered her Czech opponent from the baseline, taking full advantage of the quick conditions on centre court.
In Brisbane, Italy and Brazil were locked at one rubber apiece after the early session.
Beatriz Haddad Maia, the Brazilian world number 15, was far too strong for Martina Trevisan, dropping just two games on her way to a 6-2, 6-0 victory.
"I worked very hard to push myself to play my best tennis," Haddad Maia said. "I worked very hard in the pre-season to be as ready as I could today."
Lorenzo Musetti levelled the tie at one-all when he downed Felipe Meligeni Alves 6-3, 6-4.
In later matches, Greek world number four Stephanos Tsitsipas plays Bulgaria's Grigor Dimitrov in Perth while Britain's Cameron Norrie takes on Australia's Alex De Minaur in Sydney.
