Mannarino, Garcia steer France into United Cup quarter-finals
Journeyman Mannarino, who enjoyed his best-ever season last year, swept past Lorenzo Sonego 6-4, 6-3 before Garcia overcame a stubborn Jasmine Paolini 6-4, 5-7, 6-4.
It gave France an unassailable 2-0 lead over Italy in Sydney to put them into the knockout rounds of the mixed teams tournament.
The last quarter-final slot will be decided when Greece meet Canada, with the winner facing the best runner-up from group play in Sydney.
The Perth quarter-finals are already locked in with the Iga Swiatek-led Poland meeting China on Wednesday before Novak Djokovic's Serbia takes on Australia.
Djokovic needed treatment on a sore wrist during his win over the Czech Republic's Jiri Lehecka on Tuesday and faces another tough task against Australian number one Alex De Minaur.
The 35-year-old Mannarino won titles at Astana, Newport and Sofia last season to clock a personal best 43 wins, propelling him to a career-high 22.
After opening his season with a loss to world number seven Alexander Zverev, the no-frills Frenchman proved too hot for 46th-ranked Sonego on a scorching day at Ken Rosewall Arena.
"It's always a tough match with him and in the second set I felt it could go either way," Mannarino said. "I was lucky at four-all to go the break up and everything went my way today."
The Frenchman didn't face a break point and was solid throughout, especially on second serve, winning 13 of 18 points.
Garcia, who has slipped to 20 in the rankings after hitting a career-high four in 2018, finished the job against Paolini.
But the 29th-ranked Italian refused to go quietly, pushing it to three hard sets over 2hr 16min before Garcia served to love and banked the victory.