Rovers’ second half substitutions - made in a bid to win the game rather than settle for a draw - also contributed to the hosts’ 2-0 success at a chilly Five Heads Park.
Two goals in the last 10 minutes from Deans subs Karol Skoczen and Tommy Tierney completed a PO postcode derby double.
For Baffins, a fourth loss in a seven-match stretch which has produced just one victory further eroded their hopes of a top two finish.
Deans boss Michael Birmingham said: ‘I would like to thank the Baffins’ social media manager. He did my team talk for me.
‘The players were a little down at training after losing at Blackfield, but the Baffins social media manager did a better job in lifting them than I did. Perhaps I should employ him?!’
Birmingham was referencing a Baffins tweet that had mentioned Rovers being ‘back on the road’ ahead of the fixture - but with the word ‘road’ crossed out and ‘slope’ written instead.
The manager thought that ‘a little disrespectful’, while also admitting the introduction of George Britton and Oscar Johnston on the hour mark had helped his side.
Rovers boss Shaun Wilkinson made the attacking change - bringing on two wingers - as ‘a draw was no good to us.’
Birmingham said: ‘The Baffins subs helped us. They brought on two wide men but took off the best header of a ball on the pitch, Craig McAllister.
‘Instead of being a narrow midfield four, they played a more wide open 4-4-2.
‘That enabled Robbie Taw (at right back) to get further up the pitch.’
It was from that side that both Horndean goals arrived. The first, via an underhit back pass from Jack Williamson which Skoczen latched onto, and the second after Baffins had again conceded possession.
‘Baffins settled better,’ said Birmingham, analysing the game. ‘We didn’t expect them to start with a midfield diamond.
‘In the second half we controlled the game. I don’t think anyone could grumble that Horndean got the three points.
‘It was nice to grind out a three-pointer, with a nice clean sheet.’
Wilkinson commented: ‘It was a tight game, a cagey game.
‘We were the better side in the first half without really giving their keeper much to do.
‘It had 0-0 written all over it. I felt quite comfortable. It was always going to be decided by a mistake or something special.
‘We gave the ball away for both of their goals. That seems to be us a the moment, we’re not really making teams work for their goals.
‘You have to give credit to Horndean, they are a niggly, horrible team to play against - they work hard, they keep a good shape, they’re fit.
‘But you have to remember this is year one for this squad - the likes of Horndean and Portchester have been trying for four/five/six years to get out of this division.’
The final whistle at Five Heads Park was greeted with Horndean cheers. ‘You’d have thought they’d have won the league the way they celebrated,’ said Wilkinson.
‘This is one of the things I’m learning about this league. Everyone is desperate to beat you - it shows we must be doing something right.’
On January 26, Baffins would have gone top of the table if they had beaten Fareham. Leading 4-3 with seven minutes left, they crashed to a spectacular 5-4 defeat. They then lost at Portland and Cowes and their latest defeat dropped them to fifth.
Prior to the Fareham game, Baffins had also conceded an injury time leveller against US Portsmouth.
Taking just five points out of a possible 21, therefore, has shattered title hopes.
‘Our worst run of the season has come at the worst time,’ said Wilkinson.
‘It goes back to the US game. Instead of running the ball into the corner, we play a square pass, it gets cut out, and they score in the 93rd minute.
‘We’ve just got to try and finish the season as strongly as we can. I’d like to get 20 wins - we’ve got 18 at the minute.’
The highest Baffins have ever finished in the Wessex is fifth in 2018/19 under Steve Leigh. With Shaftesbury right on their heels with games in hand, Rovers need to start winning again - and soon - if they want to beat that position this season.