The Steelmen were cruising towards a comfortable 3-0 win until the 22-year-old was introduced for Ryan Hardie in the 62nd minute.
Tiffoney stabbed home at the back post with 10 minutes remaining before racing past the Motherwell defence and firing beyond Mark Gillespie to set up a nervy finish.
Livingston manager Holt believes Tiffoney could have a breakthrough season next year if he simply sticks to the basics.
"We know what Tiff can offer us, it's just harnessing that and adding to it," he said.
"If you give him few instructions then he causes lots of problems but when you start to pigeon hole him it can be unnatural to him and how he sees the game.
"At 3-0, it was a fantastic opportunity to let him off the leash and for him to show people what he's all about.
"I'm delighted he managed to get his two goals, if the game lasted another 10 minutes then we could have nicked that equaliser.
"I thought we were reactive in the first half and Motherwell picked up lots of second balls. Second half we were much better, on the front foot and caused them problems."
Motherwell were scintillating at times during the first half and raced into a three-goal lead courtesy of Scottish Football Writers' young player of the year David Turnbull.
The 19-year-old delivered a perfect free-kick for Liam Donnelly to glance home the early opener before doubling the hosts' advantage after a clever corner routine in the 22nd minute.
Referee David Munro gave three penalties during a crazy first half, Turnbull confidently converting to notch his 15th Ladbrokes Premiership goal of the season.
Munro then awarded both sides a spot-kick within a minute but both Hardie and Turnbull saw their efforts saved.
Motherwell's season was transformed after the winter break due to a combination of Stephen Robinson adopting a more attractive style of play and the emergence of a talented crop of youngsters, including match-winner Turnbull and Rangers-bound Jake Hastie.
Robinson admitted the development of his young players and their continued impressive performances were the highlights of the season.
"It's defined our season, credit to everybody at the football club because we stuck together during a difficult time in the season," he said.
"We managed to develop the young players, bring them back from loans and work with them in training.
"We had a difficult spell earlier in the season, although we reached the quarter-final, but the emergence of the young boys has been the icing on the cake."