Tejay van Garderen (BMC Racing) moved into the overall lead of the USA Pro Challenge after placing second behind Janier Acevedo (Jamis) on the race's key mountain stage.
Acevedo led home van Garderen in Beaver Creek after a climb-packed fourth stage of the race. The duo had broken free from former escape companions Tom Danielson (Garmin-Sharp) and van Garderen's team-mate Mathias Frank, who finished third.
Former race leader Lachlan Morton (Garmin-Sharp) rode well to finish in eighth position, but it was not enough to retain the top spot on GC.
British rider Josh Edmondson (Sky) stayed in the thick of the action to claim seventh on the stage, one minute and 28 seconds behind stage winner Acevedo.
Chris Froome (Sky) was one of the last riders home on the stage, coming in 18 minutes and 55 seconds behind Acevedo in a small group with fellow Brit David Millar (Garmin-Sharp). The 2013 Tour winner is using the race to fine tune his form ahead of the world championship road race next month.
Van Garderen leads Frank by four seconds overall, with Acevedo in third at 30 seconds. Friday's 16.1km uphill time trial favours van Garderen, and he is expected to extend his lead.
Highest placed British rider is Steve Cummings (BMC) in 38th place overall at 12-19.
The UCI 2.HC-ranked USA Pro Challenge concludes in Denver on Sunday, August 25.
Results
USA Pro Challenge 2013, stage four: Steamboat Springs to Beaver Creek, 165.6km
1. Janier Acevedo (Col) Jamis-Hagens Berman in 4-09-08
2. Tejay van Garderen (USA) BMC Racing Team
3. Mathias Frank (Swi) BMC Racing at 13 secs
4. Thomas Danielson (USA) Garmin-Sharp at 22 secs
5. Gregory Brenes (CRc) Champion System at 1-07
6. Damiano Caruso (Ita) Cannondale at 1-28
7. Joshua Edmondson (GBr) Sky
8. Lachlan Morton (Aus) Garmin-Sharp
9. Michael Schar (Swi) BMC Racing
10. Darwin Atapuma (Col) Colombia at same time
Other
36. Steve Cummings (GBr) BMC Racing at 5-08
106. David Millar (GBr) Garmin-Sharp at 18-55
108. Chris Froome (GBr) Sky at 18-55
Overall classification after stage four
1. Tejay van Garderen (USA) BMC Racing in 15-44-59
2. Mathias Frank (Swi) BMC Racing at 4 secs
3. Janier Acevedo (Col) Jamis-Hagens Berman at 30 secs
4. Thomas Danielson (USA) Garmin-Sharp at 40 secs
5. Lachlan Morton (Aus) Garmin-Sharp at 1-17
6. Gregory Brenes (CRc) Champion System at 1-37
7. Darwin Atapuma (Col) Colombia at 1-52
8. Damiano Caruso (Ita) Cannondale at 1-52
9. Rory Sutherland (Aus) Saxo-Tinkoff at 1-58
10. Lucas Euser (USA) UnitedHealthcare at 1-58
Other
38. Steve Cummings (GBr) BMC Racing at 12-19
51. Josh Edmondson (GBr) Sky at 19-46
87. Chris Froome (GBr) Sky at 34-52
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