The attacking midfielder fired home the Bees’ second of the afternoon after Andre Gray slipped and the ball fell kindly to his feet.
Alex, whose first Brentford goal came earlier in the season at Blackpool, also got the assist for his side’s third when he whipped in a corner for Jonathan Douglas to nod home.
The 21-year-old was substituted with six minutes remaining.
Elsewhere in the Championship, Ryan Fredericks played 90 minutes for Middlesbrough in their 2-0 home win against Fulham, while Grant Hall was on the bench for Birmingham City as they drew 1-1 at Charlton Athletic.
Kenny McEvoy went on as a late substitute for Peterborough United, their League One clash with Oldham Athletic at London Road ending 2-2, while there was late heartbreak for goalkeeper Jordan Archer in League Two as he was beaten in stoppage time at Wycombe Wanderers – meaning his 10-man Northampton Town side were forced to settle for a 1-1 draw.
Shaq Coulthirst played 90 minutes for Southend United as they lost 1-0 at home to Morecambe, also in League Two, while Tom Carroll was an unused substitute for Swansea City in their 2-2 home Premier League draw with Newcastle United.
In Germany, Lewis Holtby helped Hamburg claim a vital 1-0 win away at Borussia Dortmund in the Bundesliga, the midfielder playing the full 90 minutes, while Tomislav Gomelt was named on the bench for Bari as they drew 1-1 at home to Modena in Italy’s Serie B.
In the MLS, Grant Ward played 58 minutes for Chicago Fire as they drew 1-1 at Philadelphia Union on Thursday night, but the midfielder wasn’t involved in Sunday’s evening’s goalless stalemate at home to Montreal Impact.