The world number 48 from France won six of the next eight points in the deciding tie-break to defeat Monaco in two hours and 41 minutes at the Sony Open in Miami.
Chardy showed admirable fighting qualities throughout the first-round encounter, recovering from 3-0 down in the first set to win it in 49 minutes.
Monaco again started strongly in the second set, winning the opening three games, and the world number 41 from Argentina managed to build on that beginning to level the match.
The 27-year-old Frenchman was also in trouble in the third, losing his first service game before surviving three break points in his third and another in his fourth.
But Chardy's reward for beat Monaco at the ATP 1000 Masters event must seem more like a punishment as the Belgium-born right-hander will have to face world number two Novak Djokovic in the next round.
Last week, Djokovic won the BNP Paribas Open in Indian Wells, California, overcoming Roger Federer in the final.
All the seeded players in Miami have been given a bye through the first round and Federer (fifth seed) will face Ivo Karlovic first up after the Croatian defeated France's Paul-Henri Mathieu.
Karlovic won 7-6 (7-3) 7-6 (7-5) thanks to his booming serve with the 35-year-old Croatian sending down 21 aces and winning 80 per cent of points on his first serve.
Czech Republic's Radek Stepanek had a fairly comfortable day in Florida, cruising to a 6-3 6-0 win over Daniel Brands of Germany, while Cypriot Marcos Baghdatis pulled off an incredible comeback, winning the last five games to prevail 1-6 6-2 7-5 over Santiago Giraldo of Colombia.
Giraldo led 5-2 in the third set and was 30-0 up on his serve before Baghdatis won the next four points to break the Colombian.
Baghdatis won his next two service games to love to edge ahead 6-5 and then broke Giraldo for the fifth time in the match to claim his fourth first-round victory of the year.
The 28-year-old Cypriot has yet to win a second-round match and will line-up against German 24th seed Philipp Kohlschreiber next.
Australia's Matt Ebden accounted for Lukasz Kubot of Poland 4-6 6-4 6-4, while Frenchman Adrian Mannarino trumped Russia's Nikolay Davydenko 6-4 7-5 and Jiri Vesely of Czech Republic defeated Italy's Filippo Volandri 6-4 7-6 (7-1).
Albert Montanes won 5-7 7-6 (7-5) 6-3 over Michal Przysiezny, Thiemo de Bakker triumphed 6-3 6-2 against Victor Hanescu, Teymuraz Gabashvili defeated Marcel Granollers 6-4 6-3 and Alejandro Gonzalez beat Malek Jaziri 7-6 (11-9) 6-1.
Julien Benneteau recovered to win 6-7 (2-7) 6-3 6-2 against Kyle Edmund, Marinko Matosevic defeated Alejandro Falla 1-6 6-4 7-6 (8-6), Ivan Dodig overcame Andrey Golubev 4-6 6-1 6-4, Dominic Thiem knocked off Lukas Rosol 7-6 (8-6) 6-4 and Horacio Zeballos eliminated David Goffin 7-5 6-3.