Netherlands youth international is hopeful of returning to Stamford Bridge as a first teamer.
French midfielder converted from the spot after Allan Nyom had fouled Wilfried Zaha inside the box.
Valdes expected to move to Besiktas but Turkish side backtracked on agreement.
Manchester City host Watford in the Premier League on 29 August. Find out where to watch the match in the UK
Leeds had agreed a £3m deal with Watford for Italian forward before talks broke down earlier this week.
Ake signed a five-year deal with Chelsea before joining the Hornets on loan.
The 20-year-old Dutch youth international joins newly promoted club on a season-long loan.
All three promoted teams in action as the opening day of the 2015/16 Premier League season continues.
Troy Deeney remains central to Watford's plans despite the changes at the club.
IBTimes UK sports editor Nick Howson and sports reporter Tony Mogan ponder which sides are up for the drop this year.
French midfielder joined Premier League newcomers on 6 July, signing a four-year deal at Vicarage Road.
Underused French midfielder moves to Vicarage Road on a four-year deal for a club-record fee.
But the Watford goalkeeper warns Liverpool fans Firmino will need time to adapt to the Premier League.
Bomb squad detonate suspicious package in town centre.
Sanchez Flores has a busy summer ahead if he is going to build a Premier League squad.
Gomes believes Spurs have failed his compatriot Paulinho, who has struggled since arriving in England.
New book suggest two FA officials approached Taylor on issue.
Eddie Howe's side jubilant as they secure success on the final day of the season against Charlton.
The Hornets are up with a game to spare as Middlesbrough and Norwich stumble.
Manchester City have completed the signing of Jadon Sancho from Watford for £500,000.
Van Gaal has assessed Powell and is ready to send him on loan with Championship clubs Derby and Watford interested.
Chelsea boss, Jose Mourinho has apologised to referee Kevin Friend for comments he made, after the referee decided not to award Chelsea a penalty during their 3-0 FA Cup victory over Watford on Sunday.