Gloucester earned West Country bragging rights with a bonus-point Premiership win over Bath at a packed Kingsholm.
First-half tries from Henry Trinder and Paul Doran-Jones helped Gloucester into a 15-10 lead at the break, Matt Banahan replying for Bath.
Tom Biggs soon went over to level, but Gloucester won it with two Nicky Robinson penalties and a Tom Voyce try.
The match was then marred by Olly Barkley appearing to break a leg before Ben Williams and Voyce traded tries.
Victory strengthened Gloucester's grip on third place while defeat means Bath, in fourth, will slip down the table if either Northampton or London Irish win on Sunday.
It also came at a cost for Steve Meehan's men, with the game held up for around 10 minutes while Barkley was treated on the pitch after being hurt when team-mate Butch James appeared to fall on him.
But Barkley's injury, which is a suspected double fracture of his left leg, was not the defining moment of the contest as the Cherry and Whites fully deserved completing the league double over their fierce local rivals.
Such was the interest in the sold-out fixture that Gloucester fans were queuing to get in and claim their favourite spots in The Shed three-and-a-half hours before kick-off.
They were rewarded with an early Robinson penalty, with the fly-half then adding the extras when centre Trinder took advantage of scrum-half Rory Lawson's kick taking a kind bounce to go over for the game's first try.
Bath took little time to mount a response as Williams collected an exquisite James pass and broke the Gloucester defensive line to send Banahan over under the posts, Barkley adding a simple conversion.
Doran-Jones then took advantage of a Pieter Dixon error to touch down Robinson's rolling kick before Barkley ensured Bath would turn round only a try behind when he landed a penalty.
Biggs showed good strength to level the scores, but Gloucester pulled clear with two Robinson penalties before Voyce went over in the corner.
It appeared that both sides would play out time after Barkley's injury, especially when Robinson landed his fourth penalty.
But Bath pulled to within seven points when James converted Williams' try, only for Gloucester to deny the visitors a bonus point and earn one for themselves when Voyce claimed his second score against his old club.
Gloucester boss Bryan Redpath told BBC Radio Gloucestershire:
"You know there are big games in the season and they don't get bigger than the Bath derby at Kingsholm.
"We let in a couple soft tries and we missed some opportunities that could have put a bigger shine on the day but on the whole you can't take anything away from the boys, they were outstanding.
"Tom Voyce has been sat in the background for a while but he's been working very hard and I'm delighted for him today."
Bath head coach Steve Meehan:
"I think we invited Gloucester in today and they accepted the invitation.
"Our breakdown wasn't as good as it had been, or needed to be, and our decision-making to get out of our defensive third wasn't particularly composed.
"We had some good opportunities to score more tries, but our decision-making, accuracy and execution let us down. We let ourselves down and our supporters down with that performance."
Gloucester: Morgan, Sharples, Trinder, Fuimaono-Sapolu, Voyce, Robinson, R. Lawson, Wood, S. Lawson, Doran-Jones, James, Hamilton, Buxton, Hazell, Narraway.
Replacements: Molenaar for Sharples (41), Burns for Robinson (74), Pasqualin for R. Lawson (78), Thomas for Wood (78), Azam for S. Lawson (66), Harden for Doran-Jones (63), Brown for Hamilton (57), Strokosch for Buxton (50).
Bath: Cuthbert, Banahan, Williams, Barkley, Biggs, James, Claassens, Flatman, Mears, Bell, Hooper, Grewcock, Skirving, Watson, Taylor.
Replacements: Scott for Cuthbert (76), Vesty for Barkley (65), McMillan for Claassens (71), Barnes for Flatman (64), Dixon for Mears (12), Palma-Newport for Bell (78), Fernandez Lobbe for Grewcock (59), Mercer for Skirving (74).
Att: 16,500
Ref: Greg Garner (RFU).
