Boston Bob was made to work hard on his debut over fences in the opening beginners chase at Navan.

Willie Mullins charge was sent off 1/5 favourite for the two-and-a-half mile contest and settled behind the leaders as You Must Know Me cut out the running.

Ruby Walsh moved into second four from home on the hotpot and asked him to take closer order after the third last.

He tackled the front-runner at the penultimate fence but had to get serious to gain a narrow lead at the last.

The runner-up pushed him hard on the run-in and the verdict was only a half length at the line.

Boston Bob was one of the top novice hurdlers last season and his only defeat came when he was second in the Albert Bartlett Hurdle at Cheltenham.

Mullins was disappointed with the chasing debut of Graham Wylie's horse:-

"He made hard work of that and his jumping probably kept him in the race. He wasn't impressive anyway.

"We'll see how he comes out of the race but he won't be going to Leopardstown.

"It might take him some time to get over that so we won't make any plans at the moment."

Ruby Walsh added:- "It was harder than I had expected this morning but not as hard as I expected after going to the start. It was incredibly deep ground.

"It was his first run and I was delighted with the way he jumped. I thought he was a fraction cautious at home but he was brilliant today.

"We've always thought he was a hell of a good horse. It was a good start - a good clear round - and its onwards and upwards."

Ladbrokes pushed Boston Bob out to 10/1 (from 7/1) for the RSA Chase, while Stan James were also not impressed moving him out to 13/2 (from 11/2).

Stan James also introduced You Must Know Me at 20/1, and have Dynaste as their 4/1 favourite.

Boylesports (6/1), Paddy Power (7/1) and William Hill (8/1) all left Boston Bob unchanged for the RSA Chase.

(Additional reporting by Alan Magee)