After an early break Roulston worked hard to move to the chase bunch, forcing Bauer to make a solo charge from the third pack. Roulston's Trek Factory teammate Jesse Sergent then worked hard to drive through to the front of the field, and gradually the battle of attrition told.
With five laps remaining it was down to Roulston, Bauer and Davison, who did more than his share of tempo work at the front of the pack.
The trio were still together as they rounded the corner with 400m remaining. As Roulston made his move, Bauer looked to jump across to repeat his sprint finish to the 2010 title, but just failed.
"I am exhausted,'' Bauer said. "Anything but the win here is disappointing especially after a hard, hard day. I just had nothing in the kick. I completely cramped up when he [Roulston] went.''
There was plenty of joy for the young Christchurch rider, Davison, who not only clung with the two professionals for virtually the entire journey, but even fought back after being dropped on the penultimate climb up Dyers Pass Road.
``Just coming around that last corner with those two guys was a dream come true. I watched them in the Tour de France a couple of years ago over there and to be riding alongside them today was just awesome,'' Davison said.
The national under-23 honours went to Te Awamutu professional Hayden McCormick, who out-sprinted defending champion James Oram and fellow New Zealand junior representative Dion Smith.
Results:
Elite men, 185km: Hayden Roulston (Trek Factory Team, Christchurch) 4:40.39, 1; Jack Bauer (Garmin-Sharp, Takaka) same time, 2; Tom Davison (Scotty Browns Vision Systems, Christchurch) at 1sec, 3; Jason Christie (Breads of Europe-All About Plumbing, Tinwald) at 2min 28sec, 4; James Williamson (L&M Ricoh, Alexandra) at 2:39, 5.
Under-23: Hayden McCormick (Lotto Belisol, Te Awamutu) 4:47.31, 1; Dion Smith (Auckland) same time, 2; James Oram (Auckland) same time, 3.