Adam Johnson, who was carded on 12 minutes for a deliberate dive in the penalty box, curled a brilliant effort over the wall on 40 minutes to put Watford ahead.
Former Pool man Danny Shittu had earlier gone close with two headers while Jay De Merit thudded Rachubka's bar with a six-yard header.
Grayson's side - showing five changes from Tuesday's Carling Cup win against Southend - found it difficult to keep possession against the league leaders.
Pool's only real effort on goal in the first half was a David Fox left foot drive which failed to trouble Mart Poom.
Pool started the second half brightly and deservedly equalised from the spot.
Gary Taylor-Fletcher was hauled down in the box and Wes Hoolahan made no mistake from 12 yards to send the travelling Tangerine army wild.
Tommy Smith hit the bar when he should have sealed the game in the 89th minute but Pool held on for a precious point.
* SEE The Gazette on Monday for Simon Grayson's verdict.


BLACKPOOL
Rachubka, Barker, Coid, Jackson, Gorkss, Hoolahan, Flynn, Southern, Fox, Taylor-Fletcher, Morrell.
SUBS - Evans, Hills, Parker, Jorgensen, Welsh