Willie Walker reflected on a "bittersweet" afternoon after kicking the penalties that put a dent in Gloucester's Guinness Premiership title ambitions.

Fly-half Walker, on loan at Worcester from Gloucester, still has a further season to run on his Kingsholm contract – and will be eligible to play for his parent club should they reach the play-offs.

Crucially for Gloucester, he was also eligible for yesterday's Premiership derby at Sixways, and landed three first-half penalties that effectively settled the contest.

Another player with strong Kingsholm connections – former Gloucester winger Marcel Garvey – scored a try for Worcester, who defended bravely for much of the second half as the visitors dominated possession and territory.

Gloucester's inability to turn their dominance into points proved costly – and ensured Walker's accurate goal-kicking was the difference between the sides.

"It's very strange," said Walker. "I've been part of the Gloucester side for almost three years and I've been here for one month. To play against your mates and beat them is quite weird.

"It's bittersweet, because after the league finishes, I go back to Gloucester and I'm eligible for the month of May. So, ideally, when I go back, the boys will be in the play-offs!

"There was a lot of uncertainty about whether I was eligible – but apparently there weren't any clauses or anything, so I was here to play and it was a good game."

New Zealander Walker was shipped out to Worcester when Gloucester signed his compatriot, Carlos Spencer, last month. And he admitted his temporary departure had come as a surprise, particularly as he had appeared in 17 of Gloucester's 22 matches this season up to that point.

"It was a bit of a shock," he said. "I was told on the Monday that this could be a possibility – and I started training here on the Tuesday. It was a quick turnaround and quite hard to get my head around at first, but I've settled in well and the guys are a good bunch."

Gloucester started brightly, but were punished by Garvey after Spencer had missed an early penalty, Matthew Watkins had dropped Anthony Allen's pass while well placed and Olly Morgan's piercing break had ended with a loose pass. The former Kingsholm winger took Ryan Powell's pass and jinked past Will James and Rory Lawson to open the scoring.

Referee Dave Pearson then awarded a penalty try in Gloucester's favour after Worcester twice took down a five-metre scrum.

Worcester director of rugby Mike Ruddock felt the decision was "a little bit harsh", but soon replaced tighthead prop Callum Black with the more experienced Darren Morris and saw his scrum gain a degree of parity.

Spencer's conversion nudged Gloucester ahead, but they conceded three penalties in eight minutes as half-time approached – and Walker took advantage.

He made it 8-7 after Olivier Azam entered a ruck from the side; increased Worcester's lead to 11-7 when Gloucester hands strayed into a ruck – and then added a further three points when Luke Narraway was penalised for obstruction.

"You can't let anything come into your mind when you're kicking at goal," said Walker. "You just need to concentrate on what you're doing."

Spencer's penalty shortly before half-time brought Gloucester back to within four points – and incredibly no further points were added after the break. Incredibly, because Gloucester's control was almost complete. They launched wave after wave of attack in the Worcester 22 – but were undone by a combination of their own wastefulness and a solid home defence.

They looked certain to score shortly after the restart, Spencer starting and then, quite unintentionally, ending a promising move.

His initial break set the tone for Gloucester's attack, but after several phases, he was the man who lost control of the ball a few metres short.

The visitors then pierced the Worcester defence again, Iain Balshaw and Morgan combining to send Narraway away. The No 8 juggled the ball, Powell caught up with him, and as he tried to free Morgan, he lost possession two metres from the line. Gloucester were comfortably on top, but could not find a way through the Worcester defence, with head coach Dean Ryan admitting his side lack nous when James Simpson-Daniel is absent.

"We just butchered opportunity after opportunity and allowed a courageous defensive side to stay in the mix," said Ryan.

Worcester: C Latham (M Jones 16); M Benjamin, R Gear, D Rasmussen, M Garvey; W Walker, R Powell; M Mullan, C Fortey (A Lutui 67), C Black (D Morris 31), G Rawlinson, W Bowley, J Collins (N Talei 55), P Sanderson (capt), K Horstmann. Reps not used: C Gillies, J Arr, A Grove.

Scorers: Try – Garvey. Pens – Walker (3).

Gloucester: O Morgan; I Balshaw, M Watkins, A Allen, C Sharples (O Barkley 61); C Spencer (R Lamb 71), R Lawson (G Cooper 79); N Wood, O Azam (capt), G Somerville, W James (A Eustace 71), A Brown, A Satala, A Qera (A Hazell 61), L Narraway. Reps not used: S Lawson, J Forster.

Scorers: Try – penalty. Con – Spencer. Pen – Spencer.

Ref: D Pearson. Att: 12,024.