Basso has been the revelation of this year's Tour -- and the only rider to keep up with Armstrong as he powers closer to winning the showcase event for the record sixth time.
In Wednesday's 16th stage, a 15.5-kilometer (9.6-mile) Alpine time trial up to L'Alpe d'Huez, Basso did lose a significant amount of time to Armstrong -- who dominated rivals to win the 19th stage of his career.
Basso finished eighth, 2 minutes, 23 seconds behind Armstrong. He is still second overall but now trails the Texan by 3:48.
Armstrong remains confident he can hold on to win Tour No. 6, but he earmarks Basso as a serious challenger in the grueling three-week race.
"I have a ton of respect for Ivan," Armstrong said after his stage win. "I think he's the biggest threat in the race. I think he's the brightest future for the Tour."
The future had not always looked so bright for 26-year-old Basso.
Released by the Fassa Bortolo team, he joined 1996 Tour winner Bjarne Riis at Team CSC in January.
Bortolo's team manager, Giancarlo Ferretti said at the time: "We cannot keep paying so much for a rider who never wins."
In six years of professional racing, Basso had only won five low-key races after starting out with the Riso Scotti team.
But he showed great promise in the Tour, finishing with the white jersey as the best young rider in 2002. He placed 11th that year and improved to seventh in 2003.
Riis has transformed Basso from an erratic talent into a consistent performer. Dane Riis sent Basso to Boston, Massachusetts, to work on his speed, and Basso came back with an increased pedaling speed of 10 extra rotations per minute.
Riis also employed Luigi Cecchini as Basso's personal trainer. Cecchini worked with Riis when he won the 1996 Tour after a sudden, massive, improvement in his mountain-climbing ability.
Basso loves climbing.
In two stages in the Pyrenees and another on Tuesday in the Alps, he finished in the top two alongside Armstrong. He took one victory -- stage 12 from Castelsarrasin to La Mongie. His Pyrenean performances alerted fans back home.
According to sports daily L'Equipe, 3.5 million people tuned in to watch Basso on Television station RAI the following day, when he finished second to Armstrong on stage 13 from Lannemezan to Plateau de Beille.
Basso's slick riding style means he appears to expend little energy, and it has drawn comparisons to countryman Felice Gimondi, the 1965 Tour winner.
Basso is also doubtless aware that Italy needs a new cycling hero -- following the death of former Tour winner Marco Pantani from cocaine poisoning in February.
Pantani was found dead in his hotel room Feb. 14. About 10 bottles of tranquilizers were found in the room, some of them empty, others just open, police said. Pantani's 1998 Tour win was the last by a rider other than Armstrong.
Riis is confident he can help develop Basso into a Tour winner.
"He can be one of the next two winners," Riis said. "It's a question of motivation and it's up to me to help him."
However, Riis may have a fight on his hands to keep Basso. Armstrong's U.S. Postal Service team has twice tried to sign him since 2001 and is still thought to be keen. Basso would earn more money if he moved to Johan Bruyneel's Postal team, but would leave behind the formidable spirit at Team CSC.
Every winter since he took over four years ago, Riis takes his team on a weeklong nature survival course, overseen by former SAS (Special Air Service) veteran Bjarne Christiansen.
"We drop people two kilometers (1 1/2 miles) into the sea in small groups. They have to get to the shore and the one who comes last has no food," said Christiansen. "Some of them, like Ivan Basso, cannot swim. It is up to his teammates to help him and no one complains. There are no egos here, everyone is equal."
Rivals on the road, Armstrong and Basso share a bond apart from cycling.
Armstrong overcame testicular cancer to win his first Tour in 1999 -- and now wants to help Basso, whose mother is hospitalized with cancer.
"As far as what I can do for him off the bike with that situation, I'll do whatever I can," said Armstrong. "She's got a tough situation. But there's always hope."