Champions Boroughbridge suffered a cruel blow in their second match of the season when injury struck John Rowe.
The Bridge player was forced to concede two matches after picking up an arm injury in the first rubber while partnering with Kate Needham.
After winning their opening match the Rowe-Needham duo were forced to concede their two further matches, aiding a 5-4 overall victory for Thirsk.
Boroughbridge had won their opening match of the season, defeating Spa 6.5-2.5 before their bid to retain the championship hit the injury mishap. Boroughbridge broke new ground last season when they won the trophy for the first time in the club's history.
The win put Thirsk in second place on the same points as leaders Harrogate Racquets who have a better rubbers' average.
Racquets captured their second win of the season with a 5.5-3.5 win against Spa.
Match details Thirsk 5 Boroughbridge 4 (Thirsk names first): Graham Parker and Carol Collinson halved with Graeme Campbell and Suzanne Lodge 6-1 3-6; beat Ian Grasby and Cathy Farrand 6-1; beat John Rowe and Kate Needham, walk-over.
Nick Hatch and Debbie Hannam lost to Campbell and Lodge 4-6 0-6; halved with Grasby and Farrand 3-6 6-3; beat Rowe and Needham, walk-over.
Keith Philpott and Debbie Williamson beat Campbell and Lodge 6-4; lost to Grasby and Farrand 3-6 3-6; lost to Rowe and Needham 5-6 4-6.
Division One: Bedale 3 Thirsk 6; Thirsk 5 Boroughbridge 4; The Academy 4 Harlow 5; Harrogate Racquets 5.5 Spa 3.5; The Academy A 6 Bedale 3.
Division Two: Harlow A 6 Ben Rhydding 3; Ripon 5.5 Raskelf 3.5; Thirsk A 5.5 Knaresborough 3.5.
Division Three: Masham 1.5 Harrogate Racquets B 7.5; Boroughbridge A 5.5 Harlow B 3.5; Wetherby 4 Starbeck 5.
Division Four: Harrogate Racquets C 4.5 Wetherby A 4.5; Knaresborough A 5.5 Thirsk B 3.5; Harlow C 1 Birstwith 2.
Division Five: Dacre A 6.5 Wetherby B 2.5; Northallerton B 3.5 Ripon B 5.5; Starbeck A 2 Harlow D 7; Dacre A 5 Harlow D 4.
Division Six: Birstwith 7 West Tanfield 2; Raskelf A 5 Thirsk C 4; Spa A 9 Harrogate Racquets D 0.
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