Early on, Ismaila Sarr looked to get in behind the Royals back line but Rafael was off his line swiftly to slide in and smother the ball before the Hornets forward could pounce.
Reading won a free kick 30 yards out but a floated ball was easily gathered by Daniel Bachmann and Watford caught the Royals on the counter. Sarr played in Pedro and with Olise tracking back the Watford man took aim but dragged his effort wide from a difficult angle.
At the other end, Olise nearly intercepted a cross-defence pass from Troost-Ekong to Sierralta - but the latter slid in to clear just before Olise could get a toe in. Ejaria did steal possession moments later though and won a free kick which was floated towards Holmes at the back post - his central header looked for Moore but the Hornets cleared their lines as the captain shaped to hook an effort goalwards.
The hosts had the lead soon after though. Appeals for offside were dismissed when Sarr collected a direct ball on the right and he was found again with a neat pass inside. Cutting onto his left boot he curled a shot past the helpless Rafael and inside the left upright for 1-0.
A minute later it was 2-0. Again Sarr escaped the attentions of the Reading defence and from a tight angle he bulleted the ball high past Rafael and into the roof of the Royals net. 
The Royals looked to reply but a long ball looking for Meite found him - but by the time he had brought the ball down the angle was too narrow and he lashed the ball high into the stands.
Reading were playing some tidy football and Olise worked a yard to cross towards the back post and win a corner. But Bachmann punched the ball clear and Reading, although keeping possession well, couldn't force the opposition keeper into a save.
Laurent did sting the palms of Bachmann with a short from 25 yards out, but it was easy for the Hornets stopper mid-way through the first half. Laurent burst into the box moments later and took another shot at goal, but this was was dragged across goal and wide.
The woodwork denied Reading a quite superb goal back - Olise embarked on a fabulous run, beating two or three before feeding Meite to his right inside the box. He controlled the ball and fed a cross into the near post where Puscas met it but it cannoned off the right post to Watford's relief. A difficult chance but a chance.
Sarr thought he had his hat-trick when he stole in to stab home a cross from the right from 10 yards out - but the offside flag was rightly raised to deny him his third.
Bachmann did well to deny Laurent with five minutes of the first half remaining - the midfielder had scurried onto a good pass from Ejaria and powered inside towards goal but his low stabbed effort was stopped by Bachmann at the near post.
Lovely feet from Ejaria earned him a position to shoot on the edge of the box, but it was charged down and Gibson volleyed the dropping ball high and wide of the target from just outside the area.
And again Reading nearly got one back when Meite intercepted a loose crossfield ball at the back from Watford and powered past his marker and into the area. He rippled the net with his thunderous right-footed strike but it was side netting to the Royals' frustration.
Reading were finishing the half brilliantly and Yiadom scuttled into the box down the right and drilled low at the near post where Bachmann had to produce a good low save.
The visitors had enjoyed more possession and had created plenty of opportunities but Watford had been clinical in their finishing to go into the break with a two-goal lead.
Half-time: Watford 2-0 Reading
The second half started as the first had ended, Reading stealing possession and looking for a goal that would bring us back into it - but Rinomhota's clipped ball forward wasn't read by Ejaria.
A good header from Moore saw off the threat of a dangerous cross from the right. And Laurent nearly played in Pedro with a back pass that thankfully skidded behind the striker and into the palms of Rafael as intended.
Just after the hour, Lucas Joao and Omar Richards were brought on to try to change things but time was ticking away without the same amount of incident despite Reading's dominance on the ball. Ejaria won a free kick 25 yards out which Olisew struck but it was straight at Bachmann who saved comfortably.
Watford countered from that set piece and a whipped Masina cross was headed wide by Zinckernagel in the middle. Reading were running out of energy and time.
Richards chipped a cross in from the left which Joao tried to control and shoot, but he couldn't get it out from under his feet to test Bachmann. At the other end Pedro caught Holmes in the head with a challenge that seemed to see him lead with an arm, but the referee didn't see the incident.
Zinckernagel had the chance to put the result beyond doubt when a ricochet fell kindly for him but he skied his left-footed shot over the crossbar from the edge of the box.
Moore thundered into a wonderful 50:50 in midfield with Carlos Sanchez and almost set up a chance for Joao, but the Hornets buzzed around the Royals sub and regained possession. Sanchez saw a shot whistle inches wide of the left upright soon after.
Seven minutes remained when Richards hooked a hopeful shot over the crossbar from outside the box, but Saar nearly completed his treble when a cleared corner fell for the forward; he dragged a shot wide of the left post.
With his first touch of the game, Aluko nearly halved the deficit. Good work from Yiadom and Baldock on the right saw the ball centred and Moore's effort was charged down but Aluko's squirmed through and the Watford stopper did well to get down low to his right to keep it out.
Six minutes of injury time were signalled and the Royals refused to give in, crossing twice into the box from the left but the ball just not falling for Joao in the middle.
And the last chance of the game summed up the Royals' frustrations - a cross from Richards was glanced on to Baldock at the back post whose drilled cross was met by the sliding boot of Meite but he couldn't get enough on it to direct it on target.
Reading could be very proud of the performance and the effort that never relented until the very last whistle, but missed opportunities meant Sarr's strikes separated the sides.
Full-time: Watford 2-0 Reading
Watford: Bachmann, Troost-Ekong (Cathcart 70), Zinckernagel, Pedro (Gray 78), Masina, Sema (Success 78), Chalobah (c) (Sanchez HT), Hughes, Femenia, Sarr, Sierralta.
Unused subs: Foster, Ngakia, Gosling, Lazaar, Hungbo.
Yellow: Zinckernagel, Hughes
Goals: Sarr 11, 14
Reading: Rafael, Yiadom, Gibson (Richards 64), Moore (c), Holmes, Rinomhota (Baldock 87), Laurent, Ejaria (Aluko 87), Olise, Meite, Puscas (Joao 64).
Unused subs: Southwood, Esteves, Dorsett, Richards, Tetek, Semedo.
Yellow: Rinomhota