Aberdeen enjoyed most of the possession and territory but Dundee United defended well as a unit and kept their hosts largely at bay in the first half.
Ante Palaversa's drive bouncing wide was as close as the Dons got.
Shayden Morris was introduced in place of Topi Keskinen at half-time and his run and cross was beaten away by Walton with no takers for the hosts.
Jamie McGrath's low shot was awkwardly turned wide by Walton, who was unsighted as the ball travelled through the throng.
Luis 'Duk' Lopes tested Walton at his near post from the right but the narrow angle of the shot demonstrated how much United were restricting space.
Morris' pace was evident again before his deflected cross set up Sokler but the right hand of Walton clawed the ball wide.
Ambrose took over from Duk and soon had his big moment. Gavin Molloy's deep cross from the left was knocked back across the six-yard box by Nicky Devlin and the Nigerian finished emphatically.
The hosts thought they would get a chance to double that lead when Ambrose was tripped in the box by Vicko Sevelj but VAR ruled the Aberdeen forward had been offside when he received the ball.
United mustered one late chance, with Will Ferry unable to keep his effort down following Glenn Middleton's low cross.