With 13-times champion McCoy drawing a blank in his quest to reach 3,000 winners, Walsh grabbed the two vital wins so sought after by McCoy.
The highlight of his brace came as the improving Herecomesthetruth held on by the skin of his teeth to claim the Grade One Toteswinger Challengers Novices' Chase.
Massini's Maguire looked to have ended his chance with a bad blunder at the Railway Fences but fought his way back into contention and ran the 7-4 favourite to a nose at the line.
Nicholls said: "Today has been a big step up on form and he is going the right way.
"I didn't put him in any of the novice races at Cheltenham, but a race I would love to run him in is the Topham at the Grand National meeting."
Philip Hobbs said of Massini's Maguire, who pulled 20 lengths clear of the remainder: "The race didn't tell us much more about where he should be running at Cheltenham but he will either go for the RSA or the Jewson."
Walsh and Nicholls earlier struck as Celestial Halo warmed up for the Smurfit Kappa Champion Hurdle by claiming Osana's scalp as the 1-2 favourite in the Totepool Contenders Listed Hurdle.
The Triumph Hurdle winner was put in his place by Champion Hurdle favourite Binocular last time out, but managed to pick up Osana and hold off David Pipe's seasonal debutant by three and a half lengths.
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