Nadal, who is the clear tournament favourite and looks to be in the form of his life on clay this season, raced into a 3-0 lead before Spanish compatriot Almagro felt his left knee with less than half an hour played.
Rafael Nadal said he was proud and had nothing to reproach himself for after losing a top-quality Wimbledon semi-final to great rival Novak Djokovic on Saturday.
Top seed Roger Federer was finally forced to work hard for a win at the Swiss Indoors tournament as he fought back to beat Adrian Mannarino 4-6, 6-1, 6-3 in his quarter-final on Friday.
Marin Cilic overcame Federico Delbonis 6-3, 7-5, 3-6, 1-6, 6-2 after a titanic tussle in the opening singles rubber to give hosts Croatia a 1-0 lead over Argentina in the Davis Cup final on Friday.
Britain's Andy Murray enjoyed a routine win over Argentina's Juan Monaco to ease into the third round of the tennis tournament at the Rio Games on Tuesday, while Spain's world number nine David Ferrer was knocked out.
ATP Tour remembered Maradona with a social media post saying "A champion and icon loved by all", accompanied with a picture of Maradona with Federer.
Will it be Rafa versus Djoko in Sunday's final?
German 11th seed Angelique Kerber became the highest-ranked player to reach the women's quarter-finals after she outclassed Switzerland's Belinda Bencic 6-3, 7-6 (7-5) at Wimbledon on Monday.
Sania Mirza and her Czech partner Barbora Strycova stormed into the quarter-finals of the BNP Paribas Open 2017 tennis tournament with a straight-set win over their opponents in the women's doubles at Indian Wells.
Serena Williams returns to the Arthur Ashe Stadium on Sunday
Rafael Nadal, whose all-time claycourt record now stands at 414-36 says nobody should assume his feats are routine and that each victory is celebrated like the first.
Kuznetsova unable to defend Washington title over 'visa issues'
Defending US Open champion Rafael Nadal and twice winner Novak Djokovic are one victory away from renewing their rivalry in the final with both expected to get through their semis on Friday.
Images from the matches played on Day 7 at the Roland Garros on Saturday
Fifth seed Roger Federer was dumped out of the Shanghai Open, losing to Frenchman Gael Monfils 6-4, 6-7(5), 6-3 in the third round on Thursday.
Serena Williams stayed on track for an eighth Wimbledon title as she fought back to beat Italian Camila Giorgi 3-6, 6-3, 6-4 in a fiercely contested quarter-final.
Andy Murray is ready for "one more big push" this week as he tries to steer defending champions Britain into the Davis Cup final.
Roger Federer, not known for serious slip-ups in his flowing run to a record 17 grand slam singles titles, has come clean about the left knee injury that sidelined him for nearly two months.
Rafael Nadal continued his quest for a maiden Paris Masters title when he survived a second set blip to beat Uruguay's Pablo Cuevas
Novak Djokovic, Rafael Nadal and Johanna Konta progressed to the Italian Open semi-finals on Friday, but Roger Federer and Naomi Osaka were forced to withdraw with injury problems. World number one Osaka pulled out of her quarter-final meeting with Kiki Bertens due to a thumb injury before 37-year-old Federer announced his withdrawal because of a problem to his right leg.
Top seed Roger Federer needed less than an hour to dispatch Benoit Paire 6-1, 6-3 and reach the quarter-finals of the Swiss Indoors tournament on Thursday -- treating his home fans to another masterclass.
Rafael Nadal has pulled out of next week's ATP Tour Finals in London due to injury, so Novak Djokovic will end the year as world number one having returned to the top of the rankings on Monday.
Top seed and defending champion Novak Djokovic rallied to see off Frenchman Gael Monfils 6-7(4), 6-2, 6-4 in the Shanghai Open quarter-finals on Friday and world number one Rafa Nadal also booked his place in the last four.
World number one Rafael Nadal will face compatriot David Ferrer at next week's ATP World Tour Finals in London, with last year's champion Novak Djokovic and runner-up Roger Federer drawn in the second group on Saturday.
Rafael Nadal continued his perfect run on the North American hardcourts taming Czech Tomas Berdych 7-5, 7-6 (4) at the Western and Southern Open on Saturday to setup a final showdown with big-hitting American John Isner.
A summary of Tuesday's play at the French Open.
Top seed Novak Djokovic launched his Shanghai Open title defence in fine style, breezing past Spain's Marcel Granollers 6-2, 6-0 on Wednesday. Later Roger Federer, playing his first singles match since a fourth-round exit at the US Open, made a brisk return to winning ways, beating Andreas Seppi 6-4, 6-3.
Former world number one Maria Sharapova eased past defending champion Peng Shuai 6-3, 6-1 at the Tianjin Open on Saturday to reach her first WTA final in almost two and a half years.
Roger Federer took a big step towards securing his endangered place in the ATP World Tour Finals by overcoming rising Canadian talent Vasek Pospisil 6-3, 6-7(3), 7-5 in the Basel Open semi-finals on Saturday.
Serena Williams faces her first seeded opponent at the French Open on Thursday and will hope to use her booming serve to beat Australian Ashleigh Barty in the second round.
One of sport's great rivalries, Roger Federer and Rafael Nadal have clashed 37 times over the years but never stood across from each other on Flushing Meadows' hardcourts.
IMAGES from the matches played at Miami Miasters in Key Biscayne, Florida, on Wednesday
IMAGES from matches on Day 9 at the French Open at Roland Garros
Novak Djokovic lost his momentum in the second half of last season and was toppled as the world number one by Andy Murray because his work-rate dropped, the Serbian's former coach Boris Becker said on Wednesday. Speaking a day after the two terminated their cooperation by mutual consent, German Becker said Djokovic's need to spend more time with his family had derailed him on the court.
The world No 1 is certainly buoyed by the prospect of emulating his achievement of holding all four majors but knows that nothing less than perfection will be required.
Summary of sports events and persons who made news on Monday
Top seed and defending champion Roger Federer battled past in-form Russian Daniil Medvedev 6-4, 4-6, 6-4 to reach the last-16 at the Shanghai Masters on Wednesday.
Rafael Nadal gave Russian teenager Andrey Rublev a tennis lesson on Wednesday, racing into the semi-finals of the US Open with a ruthless 6-1, 6-2, 6-2 win that cleared the path for a possible showdown with rival Roger Federer.
Roger Federer cruised to a 6-4, 6-4 win over Peter Gojowczyk in his first appearance since losing in the Wimbledon quarter-finals.
IMAGES from Day 7 of the US Open on Sunday