Although they had chances, Watford were not at their best and Millwall should have capitalised in a first half in which they dominated.
The home side's determination was summed up by the hard work of Bruce Dyer as his willingness to chase long balls gave Millwall their best chances.
The big striker found himself pinned in the corner having latched on to a Zak Whitbread clearance on 21 minutes but still managed to find Barry Cogan on the touchline. Dyer was then picked out by the youngster in the box but his looping header hit the post.
The hosts could and should have opened the scoring 10 minutes later. A corner found its way to Paul Robinson on the edge of the box and his deflected shot fell to Kevin Braniff but his connection was poor and the ball went wide.
But it was third-placed Watford who would have been disappointed at half-time not to be ahead.
Darius Henderson and strike partner Marlon King were given little joy by a surprisingly solid Millwall back three, but when Whitbread failed to deal with a long ball on the stroke of half-time, Henderson slipped in Gavin Mahon for a seemingly easy chance which he put wide.
The Lions didn't let this affect them, however, and they started the second period as they started the first with Dyer having a header blocked on the line.
This turned out to be his last contribution as he was substituted five minutes later having given everything for the cause.
His replacement, Ben May, looked just as sharp and he blazed a decent 25-yard effort over the bar soon after his introduction.
Despite this only being Tuttle's second game in charge, he showed he knows his players well already and his second substitute Marvin Williams also kept the pressure on the Watford back four until the end.
But with Millwall doing much of the pressing they sometimes left themselves exposed as the game became stretched.
It took a fantastic save from Colin Doyle to keep out a Henderson header from a Matthew Spring cross on 60 minutes.
In the end, Tuttle will be pleased that his side didn't fold as they had all too often under previous boss Colin Lee and on the evidence of this performance they may still have a chance of surviving in the Championship.