Ridgers had replaced Jamie MacDonald in the first half after his team-mate picked up an ankle injury.
The substitute went on to produce a solid performance before saving penalties from Fox and Ross Callachan. Hearts won 5-4 from 12 yards, with Brad McKay scoring the decisive spot-kick.
Locke admits Ridgers' display has given him food for thought.
He said: "It will give me a headache but I've known all along. Mark's a very able deputy, he has a great presence about him.
"He came on against Raith but he did well in the pre-season games too. It's great from my point of view. I have three really good goalkeepers, there is Jack Hamilton there too.
"I was delighted with Mark's performance when he came on.
"Jamie is okay, it looks like has has just twisted his ankle a little. The physio has assessed it and he'll asses it again on Wednesday, and then we'll take it from there.
"We hope it's nothing too serious."
- Sports & Recreation
- Jamie Hamill
- Liam Fox