Williamson got her tally up and running quickly. Pressure on the Park defence allowed her to win the ball back before slotting it beyond the goalkeeper.
She added her second after winning back possession for a second time. This time she passed for Kasey Clifford to control it before sweeping the ball wide to Shannon Read. She then crossed low for Williamson to follow in and divert it goalwards.
Sumpter scored a screamer to make it three-nil. She received the ball from a throw in, turned away from her marker and struck it on the half-volley. It looped high over the Regents Park keeper and dropped perfectly under the crossbar.
Park were on the scoresheet just before the half-time break. A free-kick by Olga Suarez was palmed away by Bees goalkeeper Hannah Iguchi, Kattia Ormeno reacted quickest and drove the rebound into the net.
Brentford restored their three-goal cushion after the break. A long ball over the top was hunted down by Williamson, she got it under control before turning her marker and arrowing her shot into the bottom corner.
There was still time for Park to get another goal. They made it 4-2 when a long ball wasn't dealt with properly by Brentford's back line. Too many bounces in the final third allowed Ormano in to poke home her second of the afternoon.
Bees: Iguchi; Abou-Abdallah, McPherson-Maraj, Green, Mahamud; Azam, Clifford, Sumpter, Bah; Read, Williamson
Subs: Allidina, Idowu, Jaffer, Boparai, Williams