Heurelho Gomes made two superb saves as Watford and Chelsea had to settle for a point each at Vicarage Road.
As Chelsea stepped up the pressure with time running out, Willian and Eden Hazard combined to find Branislav Ivanovic, whose snap shot was brilliantly tipped over by Gomes, before the keeper made an even better stop to repel Diego Costa's header.
The likelihood that Chelsea will be playing European football next term receded further at Vicarage Road, despite Guus Hiddink extending his unbeaten run in caretaker charge to nine matches.
Five of Hiddink's seven Premier League games have been draws, including at home to Watford on Boxing Day, leaving the Blues 15 points adrift of fourth-placed Arsenal.
Watford were on top for much of the first half and it was a sign of frustration at things not going the visitors' way that Costa and Juan Carlos Paredes got involved in a petty exchange that saw both players booked for their amateur dramatics.
Costa made his presence felt early on by pushing Craig Cathcart to the floor and was spoken to by referee Mike Dean.
Cathcart next tracked Costa and blocked a shot, and the striker later saw an effort deflect narrowly wide off the defender. In between those efforts, Watford were well on top.
The Hornets looked for openings and the best came when Jose Holebas crossed from the left but Ighalo could not get a clean connection.
Sebastian Prodl met Ben Watson's corner with a firm header, but it was straight at Thibaut Courtois, who then denied Etienne Capoue from a promising position.
There was so much incident in the 26th minute that the anticipated ovation for Terry, who wears shirt No. 26, did not materialise.
Costa was running down the left channel when he went down softly under Paredes' challenge before reacting angrily.
The Watford right-back appeared to anticipate retribution when the pair were next in close proximity, going to ground under minimal contact. Both players were booked.
Hiddink told Costa to focus on the football and the striker almost created a goal for Oscar, only for his cutback to be prodded wide.
Troy Deeney shot narrowly wide, sending his effort across goal, before Eden Hazard tried to spark Chelsea into life. He teed up Branislav Ivanovic, but Gomes reacted instantly to tip it away.
Willian next fed Hazard, but he took a heavy touch and Gomes smothered the ball before a flying stop denied Costa from Willian's cross.