The two sides were first and second coming into the game, and the Lions knew a victory would guarantee them the title.
The hosts at Chapel Gate started well and opened up a 22-5 lead, but their visitors came back at them, narrowing the gap to 22-17 at the break.
Winchester then took the lead at 22-25, before the advantage swung back to Bournemouth with a James Kennedy try, converted by Grant Hancox.
But the Hampshire side made it 29-31 after two penalties, and Ryan Morrell crossed to send a bumper crowd wild and to confirm the title for Bournemouth.
Ryan Morrell dives over to score. (Image: Simon Carlton)
Director of rugby, Will Croker, was delighted: “What a game, what a day, what a season. It was unbelievably good.
“We possibly would have liked it to have been a little easier than it was, but the way that it finished, two committed, talented teams both going at it and for it to have been won with the final play of the match, it was the sort of stuff dreams are made of, really.
“We were very, very happy with what that picture looked like for us at the end.
“It wasn’t a great game in terms of how we executed. We had the strong wind in the first half, which we took advantage of, but we knew that they were going to come back.
Flying winger Ryan Morrell dives over to score. (Image: Simon Carlton)
“We felt it was a 15-point wind and we didn’t turn around with 15 points up.
“So we knew that the second half was going to have to be a real war of attrition. And that’s kind of how it showed up being.
“We were delighted that we managed to get past the line and Ryan scored a very good try at the end.”
Croker said the fulltime scenes were ‘fantastic and really joyous’.
Coach Will Croker with his captain Grant Hancox. (Image: Simon Carlton)
“I wish we could play in front of crowds like that every week,” he said.
“We had a huge following, both teams did, in fairness to Winchester, they brought some busloads of people along and I think everyone had a great day.
“So we wish them luck in the playoffs. We now focus on trying to go undefeated for the season.
“It’ll be an amazing way to send off the three lads that are retiring, if we can get that win away at Guildford, and then all the hard work starts looking forward to next season.”
The players celebrating with a song. (Image: Simon Carlton)
Croker praised George Cotterell, who broke his thumb in the first ten minutes and played for a further 45, while Louis Davies popped his ACJ and played the full 80 minutes.
He said: “As it was our youth and mini festival, I’d love to thank all of the volunteers that helped out with that, and to have helped out throughout the season.
“It was an amazing turnout, and we couldn’t do what we do without the volunteers, without our sponsors.
“The sponsors were there en masse. There were hundreds and hundreds of people there, and it really was an amazing way for our community to enjoy what’s been a great season.
“We’ve now obviously got the Guildford game, our Nomads have got another three matches, and then we’ll take stock, start to think about recruitment, start to think about player retention, and then what next season looks like.
“But for now, it’s just lovely to be able to sit back and really enjoy it.”