The Coleg y Cymoedd product scored the first and last try as Cardiff Blues dethroned 2015 champions Newport Gwent Dragons with a 24-22 win.
Wales’ Capital Region’s last-gasp victory at BT Sport Cardiff Arms Park ensured they qualified for the series finals in Coventry on August 7, as group winners.
Blacker, 18, said: “I can’t get over it. Just to represent Cardiff Blues at this level, so young is a massive honour for me and to go on to win the tournament is even better.
“We only had two sessions, it’s just trying to get used to playing with each other but from the start we went well and got better as the tournament went on.
“It’s just an awesome feeling to win the tournament and to beat the Dragons, last year’s winners, it’s overwhelming.
“I saw a gap, I went for it and lucky enough I got through it to get the winner.”
Cardiff Blues will be without some of their young stars from Friday’s triumph due to Wales Under-18s duty.
But Blacker still believes they have the talent to prosper at the Ricoh Arena.
He added: “It will be a massive challenge going up to Coventry, the English clubs are always good but I’m backing the boys and think we can do well.”
The Singha Premiership Rugby 7s Series finals take place at the Ricoh Arena on Sunday 7 August. For tickets and details visit premiershiprugby.com/singha7stickets
Ospreys 15 (Penalty try, Spratt, Baker)
Cardiff Blues 17 (Thomas, Jenkins, Crocker)
Newport Gwent Dragons 26 (Brew, Frewen, L Lewis, Robson)
Scarlets 12 (Davies, Pearce)
Newport Gwent Dragons 19 (Frewen, J Lewis 2)
Ospreys 21 (Andrews, Scrivens, Spratt)
Cardiff Blues 15 (Jenkins, Blacker, Beale, Roach)
Scarlets 12 (Edwards, Evans)
Ospreys 24 (Baker, Evans, Spratt, Andrews)
Scarlets 5 (Edwards)
Newport Gwent Dragons 22 (J Lewis 2, L Lewis, Levesley)
Cardiff Blues 24 (Blacker 2, Jenkins, Tomlinson)