Ronny Deila's side did not have it all their own way in Saturday's clash at Celtic Park, but Anthony Stokes' header on the stroke of half-time gave them the advantage.
Guidetti then netted his 10th goal in his last nine Celtic appearances when he finished Adam Matthews' cross from the right nine minutes after the restart.
James McPake saw an effort ruled out for offside shortly afterwards, but Dundee did hit back in the 58th minute when their own in-form striker, David Clarkson, became the first player in the club's history to score in each of his first seven games.
Motherwell looked good for at least a point when Henrik Ojamaa quickly cancelled out Billy McKay's opener in the first half, only for two goals in the space of seven second-half minutes from Marley Watkins and Josh Meekings to clinch the points for the hosts.
Third-placed Dundee United were also 3-1 victors at home to Kilmarnock, while Hamilton Academical - who are a point behind United in fourth - ended a run of four games without a win to pile more misery on lowly St Mirren with a 3-0 victory.
