Boardman, winner on the first two days, was in the thick of the action again, finishing seventh and losing just 13 seconds to his team-mate overall.
The Gan duo opened a 25sec lead over their closest challenger, Poland's Dariusz Baranowski of the US Postal Service team.
The high point of the day was the one-in-three climb of Rosedale Chimney with 40 miles to go. Hundreds of enthusiasts lined the North York Moors climb as Britain's Brite Voice team fulfilled team orders to be at the front when reaching the climb. Chris Walker, the 1993 Milk Race winner, obeyed by breaking clear after 17 miles with his team-mate Jon Clay, the German Jens Voight, Ludovic Auger of France and America's Jonathan Vaughters. By Westerdale Moor, at 54 miles, they were more than eight minutes clear.
Boardman and O'Grady spearheaded a strong chasing group that included the Festina team leader, Neil Stephens, and Baranowski.The Walker group's escape ended at Stillington with only 13 miles to go. But Clay still had enough in his legs to win a special sprint prize of pounds 1,000 at Sutton on the Forest as the leaders neared York.
O'Grady, a former Olympic and world track champion, was easily the fastest sprinter in the group, and won the stage after overcoming some rough-house tactics by Clay, who was second.
Apart from the reshuffle at the top, there was little change in the overall positions. Most of the contenders who missed the decisive break were in a group that closed dramatically on the leaders in the closing miles, finishing 18 seconds down.
Britain's Chris Newton started the day in eighth place overall, and after a good tactical ride moved up to sixth, only 53 seconds down on O'Grady.
Today the 102 survivors tackle a 116-mile leg from Manchester to Blackpool via the climbs of Holme Moss and the Forest of Bowland.Reuse content