The striker arrived from Liverpool in the summer but has found minutes hard to come by at Vicarage Road, making just one start in the Premier League.
However, he got the nod for Saturday’s FA Cup tie against Burton and his 77th-minute strike sealed a 2-0 victory for his side.
Sinclair admits he always knew that joining the Hornets would prove a challenge but is hopeful that his first goal for the club can help persuade Mazzarri that he deserves more of a shot at a run in the first team.
“Hopefully he can afford to put me in in the forthcoming games,” he said. “I always knew that coming here was going to be a work in progress, it wasn’t a matter of coming here and demanding game time. It was always a work in progress.
“I know as a young player I have things to work on and I am just trying to do that. As long as opportunities like this keep on coming I will do my best to take.”
A fan who was airlifted to hospital during Chesterfield's 3-1 defeat to Lincoln is responding well to treatment, the Spireites have said.
Neil Warnock is not letting himself dream of the Premier League despite Cardiff edging closer to promotion with a 3-2 triumph over Birmingham.
Chris Wilder thought his Sheffield United side just about shaded the goalless draw at Ipswich and enjoyed the best of the limited chances.
Paul Hurst highlighted the contribution of influential skipper Abu Ogogo after Shrewsbury beat Walsall 2-0 to stay in the top two in League One.
David Flitcroft rued another missed opportunity as League Two automatic-promotion hopefuls Mansfield let a lead slip at home for the third game in a row.
Blackburn boss Tony Mowbray believes Adam Armstrong is better than League One standard after the on-loan forward netted twice in the 3-0 win over Blackpool.