Frank soloes to stage 2 victory in USA Pro Challenge
Frank (BMC Racing Team), who claimed his third stage win this season, completed the 126.1-mile ride from Aspen to Breckenridge in 5 hours, 5 minutes and 19 seconds.
Morton, who rides for the U.S.-based Garmin-Sharp team, began the stage in 16th place in the same time as opening stage winner and former race leader Peter Sagan of Slovakia.
''I went for it, but I could keep up with Mathias at the end,'' said Morton, who has trained for many years in Colorado. ''The yellow (leader's) jersey is a nice consolation.''
Riding in his first full professional season, Morton won his first pro race earlier this month at the Tour of Utah.
Frank, who placed 33rd in the opening stage, trails Morton by two seconds.
With his victory secure, Frank, a double stage winner last month in the Tour of Austria, eased up at the line and raised his arms to celebrate - and the loss of speed may have cost him the race lead.
''For me, the stage win was the most important thing,'' said Frank. ''That's what I got, so I'm really happy.''
Sagan (Cannondale), a four-time Tour de France stage winner, finished third in the stage is also third overall, trailing by 11 seconds.
Morton, Frank and American Lawson Craddock (Bontrager) were out in front over the final 12 miles after the trio escaped from a 15-rider pack. The leaders built a 4-minute cushion with about 30 miles left in the stage.
Morton attacked the trio of leaders briefly, but Frank surged to the front and maintained his brief advantage to the finish.
''I was surprised,'' said Frank. ''Yesterday, I had a hard day with the altitude. But today I was good. It was the stage win first, not the race lead.''
Crashes and illness took several riders out of the race, leaving 121 cyclists from an opening field of 128.
Defending race winner Christian Van de Velde, a teammate of Morton's, finished 19th and is 20th overall, trailing by 46 seconds.
Reigning Tour de France champion Christopher Froome (Team Sky) finished 76th and is also 76th overall - over 16 minutes back.
The seven-day event continues Wednesday with the 106.1-mile ride from Breckenridge to Steamboat Springs.
The stage includes two climbs, including Rabbit Ears Pass - with an elevation of 9,426 feet - about 20 miles from the finish. The day will finish with a steep downhill into downtown Steamboat Springs.
The event's third edition concludes Sunday with a 72.4-mile Denver Circuit Race.