The Leicester City full-back also claimed two bonus points, totalling 14 points at The Hawthorns.
Castagne was among five defenders to secure a place in the Kings of the Gameweek line-up, which scored 153 points in a 5-4-1 formation.
And FPL managers have flocked to the Gunners man on the back of his 15-point haul.
Gabriel is the most-bought defender in the Gameweek, earning over 190,000 transfers in for a home match with West Ham United.
The left-back has been bought by 105,000+ Fantasy managers after delivering an assist and clean sheet in the Toffees’ 1-0 win at Tottenham Hotspur.
Reece James (£5.0m) secured his place in the Dream Team in the final match of Gameweek 1.