Curtis Valk, with two, and Boston Leier scored in regulation for Medicine Hat (5-8-1).
Lanigan also stopped both Kelowna attempts in the shootout
Zach Franco and Myles Bell each had a goal and an assist for Kelowna (6-5-1), while Madison Bowey also scored.
Jordan Cooke made 24 saves in taking the loss.
Medicine Hat led 3-1 heading into the third, but Kelowna directed 19 shots at Lanigan in the period as Franco equalized with 24.7 seconds left in regulation.
"It was kind of a roller-coaster there," said Lanigan. "It felt like we were kind of holding out for the initial two points during regulation.
"For us to come down and bear down in the shootout, that is what shows our offensive side of some of our players."
Franko said Lanigan was the difference.
"He was huge," said Franko. "They relied on him heavily tonight.
"He is a good goalie. He is big. He moves really well. I think that he is getting a great opportunity here in Medicine Hat."
Medicine Hat finished the night 1-for-3 on the power play, while Kelowna scored once in seven chances.
(Medicine Hat News)