But a second half fightback from Saints saw them close in before a try from Paul Diggin in the dying minutes - with Warriors reduced to 14 men after Walker was sin binned - took away the victory.
"We are gutted and obviously it was a big call at the end when we got the yellow card," said Ruddock.
"In fairness to Northampton, they were in the ascendancy and pressing hard, but we were hoping to hold out because our defence had been rock solid pretty much all the game.
"Losing a player was obviously a crucial moment and they capitalised on it as they got the try out wide using the extra man. I was proud of my players, though, I thought they were fantastic.
"A lot of people have been writing us off as no-hopers but I felt we showed a lot of hope and a lot of good things about our game.
"We had a couple of kicks that could have gone over and that would have made a difference. The margins are tight and unfortunately they didn't go our way.
"I spoke to Willie afterwards and he was comfortable with his actions in the tackle area, he competed for the ball and felt he was ok.
"But in the heat of the moment, the referees make the call and we have got to make sure we support him. We have to respect his decision and move on."
Warriors suffered opening day defeat at Northampton for a second successive season but Ruddock was proud of the show and the work of his team at the breakdown.
"We learnt a harsh lesson last season with the breakdown and coming into the game we concentrated on it," he added.
"We turned them over a lot and I felt we were going to hang on, I felt we might have to win ugly and if we kept on making tackles I felt we were going to do that.
"If they were going to beat us I told my players it has to be on the outside not through the middle, I felt our tackling around the fringes was exceptional. In the end they had to beat us using the extra man out wide.
"I can't criticise my players, I felt we were deserving of at least a draw at the end. If that is the standard we can produce more often, then we are going to be in good shape this season.
"Our application and attitude was really good, but at the end of the day we have lost so we have got to make sure we don't pat ourselves on the back. We have got to reproduce that on a regular basis and try and nail down the chances that we didn't quite get today."
Warriors lost summer signing Olivier Sourgens early in the game to a knee injury; however, Ruddock was full of praise for replacement Tevita Taumoepeau.
"Olivier has had a bit of a knee injury coming into the season, but from what I have been told the injury is not part of that. It was a separate injury to the medial ligament in a ruck," said Ruddock.
"It was a shame, but Tevita Taumoepeau came on and thought was exceptional. It's a blow to lose more players to injury, but I felt Tevita played very well."