Willie Mullins' high-class hurdler has had mixed results over fences during couple of seasons, but having run with credit when sixth in the Ryanair Chase at last month's Cheltenham Festival, he was a 5-1 shot for his Merseyside mission.
Things looked to be happening a little too quickly for the nine-year-old in the early stages of this strongly-run two-and-a-half-mile contest, but Townend bided his time before launching Boston Bob with a challenge in the straight.
His mount responded by showing a brilliant turn of foot between the second last and the final obstacle, bringing him from seventh place to a narrow lead.
He landed a little flat-footed after jumping the fence, giving a chance to both Rolling Aces and Ballynagour, but Boston Bob came back on the level to beat the former by three and a quarter lengths.
Townend said: "I thought I was in trouble a bit at the third-last, but he pulled out plenty.
"I know he's had two falls but he's actually a very good jumper, and he deserved that."
Owner Graham Wylie said: "After the Ryanair Chase, Ruby (Walsh) got off him and said he really enjoyed it, so we thought we'd bring him here.
"We thought the distance might be a bit too hot for him as he's a three-mile horse really, but what a brilliant ride by Paul.
"We started him over hurdles to get his confidence back and then Willie (Mullins) decided he wasn't going to go for the World Hurdle after his run in the Cleeve."
Mullins said: "He liked the nice ground. We gave him a break and brought him back.
"He ran very well in Cheltenham. I was happier that he ran better than his finishing position, so I thought I'd enter him in the two races here.
"It was easy to pick this race. Even though two and a half was not his trip, I thought it was a much easier race.
"We've plenty of time to go on to Punchestown. His owner might have two runners in the Gold Cup at Punchestown - On His Own and this fella."