Grand Slam Single??
http://www.baseball-reference.com/bullpen/Grand_Slam_Single
The game carried a 2-2 tie into the 15th inning, where Mets pitcher Octavio Dotel gave up a run on a Keith Lockhart triple, making the score 3-2 Atlanta.
The Mets loaded the bases in the bottom of the inning against Braves reliever Kevin McGlinchy and Todd Pratt drew a walk, tying the score at three.
Robin Ventura, the next batter, drilled a 1-1 pitch over the right-centerfield wall for a grand slam, sending the Mets players and fans into a frenzy. Ventura was mobbed halfway between first and second base by his teammates. The official scorer awarded Ventura a single on the grand slam because he only touched first base.
Another instance of a Grand Slam Single:
July 9, 1970: Dalton Jones of the Detroit Tigers loses a grand slam against the Boston Red Sox when he passes teammate Don Wert on the base paths. Jones pinch hits for Jim Price and belts a 2-2 pitch from Vincente Romo into the RF upper deck for a grand slam. However, he passes Wert between first and second and is called out, ending up with a 3-RBI single.
July 4, 1976: Tim McCarver passed Garry Maddox on the way to second base for his grand slam single.