Goals from Dale Carrick, Billy King and two from Ryan Stevenson secured the victory but St Mirren's shock 3-2 defeat of Motherwell ultimately ended the Jambos' 33-year stay in Scotland's top flight.
Hearts, who were docked 15 points at the start of the season after entering administration, begin life in the Championship next term and Locke is hopeful the experience gained in the Premiership will help his charges bounce back at the first attempt.
"The players made me very proud," said Locke. "I thought we were excellent today.
"I'm obviously disappointed at going down but I think over the course of the
season I've said all along that the young players have improved, and the hard
work that we've put in all season is now coming to fruition.
"I said to the players before the game that there's no point in us worrying about what happens at St Mirren, we've got to do what we can do.
"We have improved over the course of the season, the young players have
certainly got better and I think you have seen that today. When they all click
we're a half-decent team.
"We've had a lot to deal with this year with not being able to sign players and the 15-point deduction, but it shows that without the points deduction we'd
have been in the mix with a really young side, so it's credit to the players.
"I thought they were fantastic today. We didn't get off to the best of starts but I thought our response was really good."
While Locke takes the positives from the performance and result, his Firhill counterpart Alan Archibald was left bewildered after his side failed to capitalise on their blistering start to the game.
Kris Doolan fired them in front on five minutes and two good chances to increase the advantage were squandered before Hearts hit four without reply.
A late Jordan McMillan drive proved a consolation for the home side who now find themselves below St Mirren in the relegation play-off spot.
"We stopped doing what we were doing very well," said Archibald. "We had imposed ourselves on the game, and from an early point of view, the way we set up was to do that and the game plan was working.
"But for some reason the lads took their foot off the gas. Partly maybe to Hearts getting into the game, but I thought we let them into the game.
"Not a lot changed tactically in the game, but we just took our foot off the gas and we stopped doing what we were doing that was causing Hearts problems,
like moving the ball quickly and keeping possession. We stopped doing all those things.
"We had a couple of chances at 1-0, but as we've found all season it's vital
that you take those chances because it can make a massive difference.
"We're back in that relegation play-off spot, we've been in it before and got out of it and we've got to get out of it again.
"It's in our own hands and when we go into the split of games, something's got to give in every match. But we've got enough in there to go and get out of this spot.
"We've got a break now that probably comes at a good time, we've got two weeks before we go to face Kilmarnock, but there's not a lot in it between any of the teams."