Mileta Rajovic's double on his first Watford start was not enough to clinch victory as Coventry fought back three times to share the points in a thriller at the CBS Arena.
The Danish striker put the Hornets ahead 15 minutes after Daniel Bachmann had saved Matt Godden's penalty at the other end.
Milan van Ewijk levelled before half-time with a superb free-kick, but Udinese loanee Matheus Martins restored the visitors' advantage.
Bachmann's error led to a Wesley Hoedt own goal that made it 2-2, but Rajovic scored his second - only for Godden to equalise again for Coventry three minutes from time.