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.
The Spaniard, who has never gone beyond the quarter-finals in a grand slam, grew in confidence in the second set, however, with the backing of the home support on the Manolo Santana court and saved two break points before forcing a decider.
Juan Martin del Potro offered a wailing Nicolas Almagro a shoulder to cry on at Roland Garros on Thursday after the Spaniard's French Open campaign was cut short by a knee injury.
'I was top 10, I have more than $10 million. I'm not going to play for $50,000. It is not the reason'
Two fellow Spaniards who have already beaten him on his favourite clay surface could lie in wait for favourite and defending champion Rafael Nadal at the French Open.
Fourth seeds Leander Paes and Andre Sa progressed to the Estoril Open quarter-finals and also joining them in the last-eight pairs were Divij Sharan and Purav Raja.
Andy Murray was overwhelmed 6-3, 6-2 by Santiago Giraldo and champion Rafael Nadal showed signs of rustiness before reaching the Madrid Open quarter-finals with a 6-1, 6-4 win over Jarkko Nieminen on Thursday.
Rafa Nadal is unlikely to face the same problems Novak Djokovic had to confront against Jo-Wilfried Tsonga when the six-times French Open champion takes on Nicolas Almagro in the quarter-finals on Wednesday.
Rafael Nadal's quarter-final win over compatriot Nicolas Almagro made him only the sixth player ever to win 50 matches at the French Open. Roger Federer, his arch rival, had achieved the feat earlier in the tournament.
Rafael Nadal won his eighth Barcelona Open title in nine years with a 6-4, 6-3 victory over fellow Spaniard and fourth seed Nicolas Almagro on Sunday.
Rafa Nadal moved to within one victory of an eighth Barcelona Open title in nine years when he thrashed Canadian fifth seed Milos Raonic 6-4, 6-0 on Saturday to set up a final against fourth-seeded Spanish compatriot Nicolas Almagro.
World No 5 David Ferrer will lead Spain's bid to claim their fourth Davis Cup title in five years when the holders take on the Czech Republic in this month's final in Prague.
Rafael Nadal advanced to the final of the Mexican Open early on Saturday morning, beating fellow Spaniard Nicolas Almagro 7-5 6-4 in a clay-court slugfest.
Former World No 1 Rafael Nadal breezed through to the semi-finals of the Mexican Open on Thursday, dispatching Argentine Leonardo Mayer in straight sets 6-1, 7-5.
Canada raced to a 2-0 lead over Spain in their Davis Cup world group first round tie on Friday, pushing the five-times champions to the brink of defeat and moving to within a doubles victory of a maiden win at this level.
There is a reason why Rafa Nadal is called 'the Boss' by Nicolas Almagro and on Wednesday the ruthless claycourt king fired his fellow-Spaniard in his pursuit of a record seventh Roland Garros title.
The trio of Spaniards -- Rafa Nadal, David Ferrer and Nicolas Almagro -- showed why the nation has ruled Roland Garros for most of the last decade.
Spain captain Alex Corretja has defended his decision to pick Nicolas Almagro for the Davis Cup final after the holders were beaten 3-2 by Czech Republic when Almagro lost the decisive singles rubber to Radek Stepanek on Sunday.
The Czech Republic beat holders Spain 3-2 to win the Davis Cup for the first time as an independent nation when Radek Stepanek overcame Nicolas Almagro in four tough sets before a raucous home crowd on Sunday.
The Czech Republic beat holders Spain 3-2 to win the Davis Cup for the first time as an independent nation when Radek Stepanek overcame Nicolas Almagro in four tough sets before a raucous home crowd on Sunday.
The Czech Republic's Tomas Berdych brought the hosts level at 1-1 with holders Spain in the Davis Cup final with a battling five-set victory over Nicolas Almagro on Friday.
World number five David Ferrer overwhelmed local favourite David Nalbandian 6-1, 6-4 on Saturday and will meet holder Nicolas Almagro in Sunday's all-Spanish Buenos Aires Open final.
Edmund sailed through in straight sets 6-3, 6-4 against world number 70 Jeremy Chardy and will face fourth seed Dominic Thiem of Austria.
British hopeful Andy Murray won his quarterfinal on Thursday at the Olympics, delighting a Wimbledon crowd that featured Prince William and wife Kate.
American John Isner won the US men's clay court championship in Houston with a 6-3, 7-5 win over top seeded Spaniard Nicolas Almagro on Sunday.
World No 1 Novak Djokovic powered into the semi-finals of the Indian Wells ATP tournament with a commanding 6-3, 6-4 victory over Spaniard Nicolas Almagro on Thursday.
Images from Day 9 of the Australian Open on Tuesday.
Two-time winner Marin Cilic of Croatia has been ruled out of the 2012 Chennai Open, India's only ATP World Tour event, due to an injury.
World number five David Ferrer cruised to a 6-2, 6-3, 7-5 win over Tomas Berdych to put defending champions Spain level with the Czech Republic at 2-2 in the Davis Cup final on Sunday.
The Czech Republic's Tomas Berdych brought the hosts level at 1-1 with holders Spain in the Davis Cup final with a battling five-set victory over Nicolas Almagro on Friday.
Nicolas Almagro's chances of making next month's World Tour Finals in London were dealt a blow when he was beaten 6-3,7-5 by top seed and Spanish compatriot David Ferrer in the quarter-finals of the Valencia Open on Friday.
Top seed David Ferrer will meet former world number three David Nalbandian in the final of the Auckland Open after they both advanced with easy semi-final victories on Friday.
World number one Rafa Nadal notched up his 500th career win on Saturday and clinched a place in the Barcelona Open final by beating unseeded Croatian Ivan Dodig 6-3, 6-2.
Defending champion Roger Federer made heavy work of reaching his 27th consecutive Grand Slam quarter-final with a 6-3, 3-6, 6-3, 6-2 win over Tommy Robredo at the Australian Open on Sunday.
World No 5 David Ferrer claimed his 13th career title with a 4-6, 6-3, 6-2 victory over fellow Spaniard and 2011 winner Nicolas Almagro in the Buenos Aires Open final on Sunday.
Rafael Nadal zipped around Court Philippe Chatrier as though he had rockets in his heels on Wednesday during a straight sets quarter-final win over Nicolas Almagro but he was still not quick enough for the umpire.
World No 8 Robin Soderling, the highest-ranked player left in the Barcelona Open after a slew of withdrawals, sprinted into the quarter-finals with a 6-3, 6-2 win over Spain's Feliciano Lopez on Thursday.
Big-serving Milos Raonic of Canada did not dish out his best tennis today, but still he managed to book his place in the semifinals of the Chennai Open by defeating Israel's Dudi Sela in straight sets. He will now face second seed Nicolas Almagro of Spain, a 4-6, 7-6 (10-8), 6-4 winner over Japanese qualifier Yuichi Sugita. Meanwhile, defending champion Stanislas Wawrinka of Switzerland crashed out.
Indian ace Mahesh Bhupathi and Max Mirnyi sailed into the second round of the men's doubles at Wimbledon, scoring a straight-set victory over the Argentine duo of Maximo Gonzalez and Sebastian Prieto in London on Thursday. The fourth-seeded Indo-Belarus pair won 7-5, 6-1, 7-5.
Nicolas Almagro pummelled fellow Spaniard Fernando Verdasco into submission at the French Open on Monday to set up a quarter-final showdown with Rafael Nadal.