Walker was in good touch with the boot for Worcester
Worcester ended London Irish's faint hopes of reaching the semi-finals of the LV= Cup following a Pool 4 victory.
The hosts took the lead when Dale Rasmussen's strong run set up winger Chris Pennell to touch down for a try, converted by Willie Walker.
The fly-half added two penalties, while opposite number Ryan Lamb reduced the deficit to 13-6 at half-time.
Walker kicked two further penalties to extend Worcester's lead before Peter Hewatt scored with a consolation kick.
Worcester skills and backs coach Billy McGinty:
"Obviously it was a welcome win but ever since we finished the last round of Guinness Premiership matches we have tried to rest people.
"Last week at Gloucester was the first time that everyone has come back together as a team and we were really disappointed in our performance, but we have worked on a lot of things and we are pleased now.
"You get a win and you gain some confidence. We are aiming towards next week and, after today, we will be able to take it forward."
London Irish head coach Toby Booth: "At the set-piece we struggled where normally we don't.
"Credit to the opposition, but there was also the referee's interpretations and that put us behind the 8-ball a little bit.
"We are talking about consistency from us and the referee. Unfortunately, there was not a lot of that consistency so I am disappointed for the people who have travelled from our end to watch that and braved a bitterly cold afternoon."
Worcester: Latham, Pennell, Rasmussen, King, Garvey, Walker, Arr, A. Black, Lutui, Taumoepeau, Rawlinson, Gillies, Cracknell, Sanderson, Horstmann. Replacements: Jones for King (47), Gear for Garvey (67), Powell for Arr (62), Mullan for A. Black (46), Fortey for Lutui (36), Sourgens for Taumoepeau (53), Bowley for Gillies (62), Collins for Sanderson (70).
London Irish: Hewat, Ojo, Seveali'i, Mapusua, Rudd, Lamb, Lalanne, Murphy, Buckland, Rautenbach, Garvey, Perry, Johnson, Thorpe, Roche. Replacements: Catt for Mapusua (62), Lennard for Lamb (56), Richards for Lalanne (62), Dermody for Murphy (54), Coetzee for Buckland (78), Tideswell for Rautenbach (46), Low for Perry (78), Gibson for Thorpe (53).
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