Watford
On 31 January 2008, Eustace joined Watford from Stoke City for a fee of £250,000. On 20 September 2008, Eustace "scored" a bizarre opening own goal in the game between Watford and Reading, where a goalmouth scramble saw the ball go nowhere near the goal line, despite the linesman flagging for a goal to the bemusement of everyone in the ground. A corner from Stephen Hunt bounced off of Eustace and was hooked back by Noel Hunt. What could have been a debatable corner for Reading, initially given as a goal kick, was actually then given as a goal. The game ended Watford 2–2 Reading.
On 9 March 2009, he joined Championship rivals Derby County on loan until the end of the 2008–09 season, in order to help solve the Rams' midfield injury crisis. He made his Derby debut in the 1–1 draw away to Southampton, and scored against his parent club on the final day of the season. Eustace was unable to secure a permanent move to Derby at the end of his loan spell with the club and returned to Watford at the beginning of May. However, Derby manager Nigel Clough said "He's got a year left at Watford. If he's still in the same situation at the start of next season, needing a loan, then we might look at that."
With his Hornets career seemingly in jeopardy, Eustace signed an amended contract stipulating that he would not receive his sizeable appearance fee, freeing up Malky Mackay to pick the tenacious midfielder. Eustace went on to play a key role as Watford retained their Championship status for another season. He was also given the captaincy on a number of occasions with first-choice skipper Jay DeMerit sidelined through injury. Eustace made over forty appearances in league and cup competitions and was the 'Player's Player of the Season' as voted by his peers.
After much speculation throughout the 2009–10 off-season, Eustace finally signed a new two-year contract with Watford. Eustace and Mackay later revealed that he had passed a medical at Leeds United, and that there was interest from other clubs.
Ahead of the season, Mackay handed Eustace the captaincy, after DeMerit was released on a Bosman transfer. He started the season in good form, scoring Watford's first goal of the season in a 3–2 win at Norwich City, followed a week later with an over-head finish in a 2–2 draw against former club Coventry which was later named as the 2010–11 goal of the season. Eustace kept the captain's armband following the managerial appointment of Sean Dyche in June 2011 and signed a new two-year contract until 2013 at the end of July despite interest from Derby County.
In June 2013, Eustace was offered a new contract with a player/coach role, which he declined, stating that he was not ready to turn away from playing just yet, therefore leaving the club as a free agent.
