"It's a huge relief, because you look at a lot of relegated clubs who came down in the last three or four years," Boothroyd said after Sunday's game.
"Birmingham and Sunderland bounced straight back and that's an amazing credit to them, but there are a lot of bigger clubs than us who have come down, lost their momentum and ended up going down even further.
"We've got in by one goal and given ourselves a chance of reaching the goal we set out at the start of the season. We've got to enjoy this and then focus on our next game.
"Form goes out of the window in the play-offs. It's about big-game players and being big, strong and organised and keeping our nerve.
"That's what we've got to do and we've got as good a chance as any of other three sides."