Adriano Malori (Movistar) came out on top on Stage 5 of the Tour de San Luis, an individual time trial.
The Italian set a time of just over 20 minutes to take the win on the day.
Michal Kwiatkowski (Etixx-QuickStep) came in just four seconds behind, while GC leader Daniel Diaz (Funvic) did his chances no harm at all with a solid tenth place finish.
The first half of the 17.4 kilometre course was downhill with the help of a tailwind, and Malori used the conditions to good effect as he swept the rest of the field aside.
Several riders were looking threatening at the halfway mark but the headwind on the homeward leg put paid to their chances.
However, Diaz, not known for his time trial ability, managed the conditions superbl and managed to put more time between himself and his rivals for the overall title.
He now sits 1'09" clear of Rodolfo Torres (Colombia) and 1'25" ahead of Nairo Quintana (Movistar).
However, the Argentinian national champion remained cautious when talking about his chances of holding onto the leader's jersey for the remaining two days.
"Honestly, I didn’t expect this. When I crossed the line, I was even asking if I’d done enough to keep the jersey. I really didn’t think I’d gain time.
"It’s a short, intense stage (tomorrow) and the last climb is so long that you could easily lose a lot of time," he said.
"And Nairo [Quintana] has a very strong change of rhythm, so tomorrow will be difficult for me."
Meanwhile, Malori was delighted to start his season with a victory.
"The last few kilometres were tougher than I expected with the false flats and the headwind, and I wasn’t sure of my form, but there’s no better way to start the new season than with a win."
"I came fifth in the time trial here last year and then I went on to have the season of my life, so let’s hope I go even better in 2015."
Stage 6 is a relatively short 117.5 kilometre stage from Achiras to Filo Sierras Comechingones.