Latvia took a 2-0 lead over India in the Billie Jean King Cup playoff tie with wins for Jelena Ostapenko, Anastasija Sevastova over Ankita Raina and Karman Kaur Thandi respectively.
Rublev clinched his first win against third-seeded Nadal on his first match point with a typically powerful winner on forehand — a weapon Nadal struggled to contain all match.
India take on higher-ranked Latvia in their first-ever Billie Jean King Cup playoff tie. The matches will be played on indoor hard courts in an empty stadium.
World number one Djokovic was broken five times by the Briton in their last-16 clash and suffered his first loss of the year, having won the Australian Open for the ninth time in February.
Monte Carlo Masters: Stefanos Tsitsipas strolls into last-16; Novak Djokovic to face rising star Jannik Sinner
Tsitsipas, who had been given a bye into the second round, took just one hour and 24 minutes to beat 29th-ranked Russian Karatsev.
Madrid will host two groups, two last-eight ties, the semi-finals and the final.
If the 74 unforced errors were not incriminating enough, Paire's latest post-mortem on tennis in a world of Covid-19 was as explosive as ever.
The 15th-seeded Kudermetova dominated from the outset to claim a 6-4, 6-2 victory over Kovinic, ranked 91 in the world.
Rafa Nadal is aiming for a 12th Masters title in the principality ahead of his pursuit of a 14th French Open success and a record 21st Grand Slam.
Monfils, the runner-up in Monte Carlo to Rafael Nadal in 2016, was scheduled to face Pablo Andujar in the first round.
Veronika Kudermetova knocks out dark horse Paula Badosa to set up final against Danka Kovinic in Charleston
Kudermetova, the 15th seed from Russia, overcame her nerves to beat Badosa 6-3, 6-3 and reach her second final of the season.
Nadal has 71-5 record in Monte Carlo where he has fallen short of the quarter-finals just once - on his debut in 2003 as a 16-year-old.
Billi Jean King Cup: We are hungry, upsets do happen in team events in tennis, says India captain Vishal Uppal ahead of tie against Latvia
Asked about the approach the team will adopt, considering their superior rivals, Uppal oozed confidence.
Charleston Open: Ashleigh Barty overcomes American Shelby Rogers in three sets to book quarter-final berth
Barty moves on to the quarter-finals where she will face Spain's Paula Badosa, a 6-3, 6-3 winner over Caty McNally of the US.
The 90th-ranked Musetti won through 6-1, 1-6, 7-6 (10/8) after two hours ten minutes on court in Sardinia against Evans, ranked 32.
The French Tennis Federation said it hoped the delay could enable more fans to attend if COVID-19 restrictions are eased by then.
Last year's French Open was delayed by four months and held in September and October instead of its longstanding May-June slot.
Sania was selected in the TOPS during the 56th meeting of the Mission Olympic Cell in New Delhi.
Federer hasn't won a tour clay title since Istanbul in 2015; his most recent Masters triumph on the surface was Madrid in 2012.
Both world No 136 Nagal and world No 124 Kovalik came into the main draw through qualifying rounds and the Slovak prevailed 3-6, 6-1, 6-3 in a contest that lasted for two hours and 13 minutes.