Beating another play-off contender, Swindon Supermarine, by the odd goal in five at The Simply Health City Ground.
Winchester fell behind to a 15th minute cross-shot from Connor Thompson.
But a minute before the break, City equalised when Jamie Barron netted from the penalty spot.
Swindon were reduced to ten-men almost immediately after the break when Zak Westlake was sent-off for a second bookable offence.
To rub salt into `Marine wounds, one of their former players, Oli Bailey, made it 2-1 with a fine individual effort.
However, the ten-men levelled in the 65th minute, thanks to a Josh Parsons free-kick.
But Winchester won it 2 minutes from time when Barron converted again from the spot to seal a 3-2 win.
Mangotsfield United`s first win in six league matches moved them off second-bottom spot.
The Mangos won 4-2 at Paulton Rovers, who are now just a point and a place above them.
Paulton`s Camen Harvey was given straight red for poor challenge after just 18 minutes to make it a backs-to-the-walls job for the home side.
And the Mangos opened the scoring on 34 minutes as Cameron Allen scored on the counter attack.
Rovers got a goal back 3 minutes before half-time through Kailan Gould.
And just 2 minutes into the second half, Gould scored his second to give the ten-men the lead.
But 9 minutes later Mangotsfield were level, courtesy of a Josh Ford own goal.
On on 59 minutes, sub George Lloyd made it 3-2 and less than a minute later, Kane Simpson made it 4-2 with an effort from the half-way line!
Yate Town made it seven games without defeat but were pegged back late on by visiting Cinderford Town in a 2-2 draw.
The Bluebells took a 27th minute lead through Lewis Leigh-Gilchrist.
A Harvey Rivers own goal pulled the Foresters back on level terms immediately after half-time, only for Leigh-Gilchrist to restore Yate`s lead 7 minutes later.
But Cinderford earned a late point, thanks to an 86th minute Craig Norman effort.
By Steve Whitney
Keep up-to-date with our exclusive email newsletters.
Subscribe