Grady Diangana came closest for netting for the visitors, whilst Ismaila Sarr and Dapo Mebude were guilty of wasting a number of opportunities for the Hornets in a game that deserved more than a goalless scoreline.
Ismael once again shaped his side up in a 3-4-3 formation, with the boss naming arguably his strongest side of available players, barring Matheus Pereira - who is still expected to depart this summer.
Dara O'Shea took the place of Cedric Kipre in the starting line-up, with no other changes in the XI from the 2-0 win over Sheffield Wednesday.
The start didn't offer much a pre-season feel to it, with Ismael instructing his side to press their Premier League opponents high up the pitch.
Albion's start was energetic, but it was Watford who saw the first big chance of the game fall their way after catching the visitors out with a long ball over the top.
Kyle Bartley was beaten in a foot race by Cucho Hernandez who found his opposite winger Sarr in the centre of the six-yard box, but the wide man's strike to tamely trickle wide for a goal kick.
It was then Albion's turn to show a lack of sharpness in front of goal, after Conor Townsend's brilliant ball found Diangana alone in the middle of the penalty area, but his attempted lob was claimed easily by ex-Albion goalkeeper Ben Foster.
Albion threatened several times with wide balls into the host's box, but the first header to truly trouble the Hornets came just ahead of the half-hour mark with Kyle Bartley seeing his attempt go marginally off-target.
It was a feisty encounter, summed up by Dara O'Shea's challenge on Hernandez, rightly earning the young defender a booking and also gifting the hosts a glorious chance to level from the following free-kick.
Dan Gosling's strike from the left flank went right through to goal, only for Townsend to clear off the line, before the wing-back did so once again from Hernandez's acrobatic follow-up before the halftime whistle sounded.
The hosts started the second half much sharper as they looked to break the deadlock.
The first opportunity came as Sarr broke through on-goal, only for Jake Livermore to put in a pinpoint challenge for which the referee rightly waved away appeals for a spot-kick.
Dapo Mebude then should've opened the scoring only to fire wide, before David Button was called into action to save smartly from Sarr.
Both sides then made a raft of changes over the second half as they looked to provide opportunities for the rest of their respective squads.
Callum Robinson came closest to scoring for the visitors in the second half but his low strike well-saved by substitute goalkeeper Rob Elliot.
The visitors finished the brighter of the sides, but couldn't find a way through a well-drilled Watford backline to find a late winner.
West Brom (3-4-3): Button; Ajayi, Bartley, O'Shea; Furlong, Livermore, Mowatt, Townsend; Grant, Diangana, Phillips.
Subs: Palmer, Clarke (O'Shea '64), Kipre (Ajayi '64), Taylor (Bartley '72), Ingram (Furlong '81), Castro (Livermore '72), Sawyers (Mowatt '72), Gardner-Hickman (Townsend '81), Tulloch (Diangana '60), Zohore (Phillips '60), Robinson (Grant '60).
Watford (4-3-3): Foster, Ngakia, Troost-Ekong, Cathcart, Masina, Etebo, Cleverley, Gosling, Sarr, Deeney, Hernandez
Subs: Elliot (Foster '45), Andrews, Abbott, Hall, Trialist (Masina '9), Smith, Crichlow, Mebude (Cleverley '45), King, Pochettino, Goulding, Muwonge, Langston, Hunter, Forde, Wise.