Watford were denied a seventh straight win and a chance to edge closer to an immediate return to the Premier League as Middlesbrough struck late to earn a 1-1 draw.
Having beaten Sheffield Wednesday 1-0 on Good Friday, Xisco Munoz's men looked to be heading for victory by the same scoreline at the Riverside Stadium, after Ismaila Sarr gave them the lead in slightly fortuitous circumstances (32).
But though Boro struggled in the final third throughout the majority of proceedings, they gave a good account of themselves and pulled level late on when substitute Yannick Bolasie headed home Paddy McNair's free-kick (78).
Second-placed Watford extended their advantage over Brentford and Swansea in third and fourth to 10 points with six games left to play, while Boro are now nine points outside the top six.
How Watford were held on Teesside
With a valuable three points at stake for two sides firmly within the mix for promotion, it was a cagey, uneventful start to proceedings on Teesside, with few clear-cut chances in an open first half-hour.
But then, all of a sudden, Watford edged ahead in dramatic circumstances. Boro goalkeeper Marcus Bettinelli first produced an impressive save to deny Ken Sema, but Marc Bola's clearance fell kindly for Zinckernagel, who took control, though there were suspicions of handball as he did so.
As he powered a shot at goal, the ball ricocheted off the boot of Sarr and found its way past the wrong-footed Bettinelli, who was visibly aggrieved at the awarding of the goal. Appeals for offside from the hosts followed, though replays showed several Boro players were, in fact, playing the Senegalese international onside.
Though they contained the Hornets' potent attack, Middlesbrough found it difficult to threaten themselves and ended the first 45 minutes without a shot on target. Five minutes after the restart, however, Duncan Watmore had the ball in the net, only to see his close-range effort chalked off, this time for a correct offside call.
As the second half wore on, Watford's game management continued to limit Boro and they should have wrapped up all three points when Joao Pedro curled a low shot the wrong side of the right-hand upright after neat interplay on the edge of the 18-yard box.
With their first shot on target in the game, the hosts finally levelled with 11 minutes to play, when Paddy McNair found Bolasie with a free-kick that had been cheaply conceded by Ken Sema and the Everton loanee headed in to earn his side a deserved share of the spoils
Man of the match - Grant Hall
Sky Sports' Don Goodman:
"I don't think there was a better player on the pitch - he was excellent in every way. Boro, as a unit, have snuffed out a genuine threat and not many teams have been able to do that so far this season."
What the managers said...
Middlesbrough's Neil Warnock: "Watford are absolutely flying, six games on the trot before today. We had to play as if we were going away from home, structurally we were proper. It might have looked negative but they'd have passed through us. We tried to catch them on the break as much as we could. The goal did us a bit. We thought handball.
"Yannick was coming over to take the free-kick and I told him to get in the box and he scores. There were a lot of pluses today. We could easily have won the game in the end."
Watford's Xisco Munoz: "From the first day we have been positive. Step by step we are working. The first step is to get the play-off positions, then the second aim is to get second place and the next aim is to get the top position. We have to keep going. I am sure we will have difficult moments, but what is most important is we keep going. Our team has good numbers, we need to play with the same ambition.
"Sometimes we have difficult moments. Today was a tough game. We didn't have a lot of chances. They are a very good team, strong, power and speed, like us. We try always to win the games, but it is difficult to get points in the Championship.
"I don't think about the others, we will see what happens after. Most important thing is we have found focus and power in our team. We have a very good challenge. We have great ambition."
Watford are back in action at 7.45pm on Friday, April 9 when they welcome Reading to Vicarage Road - in a match live on Sky Sports Football - while Middlesbrough travel to Oakwell to take on Barnsley at 3pm the following day.