Birthday boy John Crawley pointed to the Hampshire Hawks' mid-summer run of ten wins in 11 games as the key to their promotion.
Hampshire skipper Crawley celebrated promotion to the National League's first division on his 32nd birthday - two years after Robin Smith had captained the county to championship promotion on his 38th.
"I feel more like 42, it's been a tough season," laughed Crawley, after an 11-run defeat that made it a bitter sweet day at Derby.
He added: "It has put a tinge of black on what should be a silver day but we have got be realistic and realise that over a season you're going to lose a few games.
"It wasn't the note we wanted to sign off on but the league system is based on performances over a season.
"Our two main aims were to get promotion in the championship and the one-day league. Unfortunately the championship season fell apart midway through and it's a great thing for us that we had that fantastic run of ten wins in 11 games, which stood us in good stead. It put us right at the top of the division.
"Taking a little bit of success out of the season and achieving 50 per cent out of what we set out to do is a brilliant feeling."
Crawley admitted that losing the toss was crucial yesterday as Derbyshire had first go on a slow wicket.
He added: "I thought Derbyshire performed very well on that surface and all credit to them. It obviously wasn't a perfect one-day wicket, it was slow and took a lot of turn and bounce from slower balls as well."
The champagne was flowing in the visitors' dressing room at Derby yesterday - but only after a post mortem on an embarrassing collapse and only because Middlesex had lost at Durham.
"The chase was not good, we've already talked about it," added Crawley. "We analysed the game before we celebrated promotion, we lacked a bit of responsibility in getting in but not seeing it through to the end
"We knew quite early that Middlesex had lost, just after I got out but we were still desperately trying to win the game.
"We wanted to finish the season on a good note but we didn't field as well as we have done. I thought we were a little below par against Middlesex last week and even more below par today.
"That was probably down to a bit of lethargy and tiredness coming in towards the end of the season."
Manager Paul Terry added: "It was a pretty poor performance from us in the last 15 overs. We were following the Middlesex game on the internet and whether that had an effect I don't know but losing like that was not the ideal way to go up."
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