Breakaway rider Emmanuel Guevara claimed a superb solo victory on stage five of the Tour de San Luis as second-placed Daniel Diaz assumed overall leadership of the race.
Argentine Guevara (San Luis Somos Todos) escaped from the peloton along with Martin Hacecky (ASC Dukla Praha) early in the 170km route from Juana Koslay to Carolina and the duo opened up a gap of almost 18 minutes at its peak.
However, they wilted badly as they neared the summit of the category-one Cerro el Amago 17km from the finish and their gap tumbled.
Hacecky was unable to maintain the pace and dropped off, but Guevara powered on and resisted being caught by just 15 seconds.
Numerous riders darted off the front of the bunch on the climb, including Alberto Contador (Saxo-Tinkoff), but it was Diaz (San Luis Somos Todos) who launched the most purposeful attack and although he narrowly missed out on the stage win, his efforts were enough to open up a 17-second gap at the top of the general classification.
Colombian climber Miguel Angel Rubiano Chavez (Androni Giocattoli) claimed third on the day, while Contador finished sixth in a group also containing Tejay van Garderen (BMC), who moves into second in the GC. Contador climbs to fifth.
Overnight leader Michal Kwiatkowski (Omega Pharma - Quick-Step) had a difficult day and dropped to ninth in the standings after crossing the line three minutes 46 seconds down on Guevara.
Saturday's sixth stage takes the riders on a mountainous 156km route from Quines to Mirador del Sol.
1 Emmanuel Guevara (Arg) San Luis Somos Todos, 4:17.48
2 Daniel Diaz (Arg) San Luis Somos Todos, +15secs
3 Miguel Angel Rubiano Chavez (Col) Androni Giocattoli, +1.17
4 Arnold Alcolea (Cub) Cuba, same time
5 Javier Acevedo (Col) Jamis-Hagens Berman, +1.21
6 Alberto Contador (Spa) Saxo-Tinkoff, st
7 Tejay van Garderen (USA) BMC, st
8 Alex Diniz (Bra) Funiv Brasilinvest, st
9 Mauro Santambrogio (Ita) Vini Fantini, +1.41
10 Matteo Montaguti (Ita) Ag2r-La Mondiale, +1.42
1 Daniel Diaz (Arg) San Luis Somos Todos, 16:49.52
2 Tejay van Garderen (USA) BMC, +17secs
3 Alex Diniz (Bra) Funiv Brasilinvest, +39
4 Alberto Contador (Spa) Saxo-Tinkoff, +1.04
5 Jurgen van den Broeck (Bel) Lotto-Belisol, +1.07
6 Miguel Angel Rubiano Chavez (Col) Androni Giocattoli, 1.47
7 Vincenzo Nibali (Ita) Astana, +2.14
8 Mauro Santambrogio (Ita) Vini Fantini, +2.17
9 Michal Kwiatkowski (Pol) Omega Pharma - Quick-Step, +2.19
10 Javier Acevedo (Col) Jamis-Hagens Berman, +2.20