Marshall lowered his shoulder into North Carolina State's Alex Johnson to clear a path, but no foul was called and the Tar Heels survived to set up a tournament title confrontation with No. 17 Florida State.
Florida State prevented a championship meeting between old rivals North Carolina and Duke by surprising the sixth-ranked Blue Devils in the second semifinal 62-59.
A desperation 3-point attempt at the buzzer by Duke's Seth Curry from midcourt bounced off the back of the rim to leave the Seminoles as the upset winner.
North Carolina overcame a six-point deficit early in the second half in a game that had 15 lead changes, but could not shake the Wolfpack. North Carolina State took a 67-66 lead with 1:08 remaining when DeShawn Painter made 1-of-2 foul shots, but Harrison Barnes did the same for North Carolina with 59 seconds to go to forge a 67-67 tie.
Lorenzo Brown then turned the ball over for the Wolfpack, giving the Tar Heels a chance to win it in regulation.
After Marshall made his go-ahead shot, North Carolina's Justin Watts picked off a pass along the baseline to all but seal the victory.
Although there was no foul on Marshall during the critical play, the officials did make 42 foul calls. Both teams' leading scorer fouled out -- Tyler Zeller for North Carolina and C.J. Leslie for the Wolfpack.
Zeller scored 23 points while Barnes had 16 for the Tar Heels (29-4). Leslie had 22 points before leaving the game. North Carolina State fell to 22-12.
In the second semifinal, Michael Snaer's 3-pointer put Florida State in front for good with 3:31 to play, but the contest went down to the wire and almost went into overtime.
Duke closed within one with 47 seconds to go on a layup by Austin Rivers, but Luke Loucks hit a jumper for the Seminoles at the end of the shot clock to account for the final score.
Rivers then missed a 3-point try for Duke, but the Blue Devils got another chance when Curry stole the ball at midcourt. He launched the ball toward the basket as the horn sounded and barely missed going in.
Florida State (23-9) was led by Snaer with 16 points. It was the Seminoles' fourth straight victory. Rivers had 17 for Duke (27-6), which split its two regular-season meetings with Florida State.