Beau Mertens has had a mixed day at Caulfield, closing the gap on jockeys' premiership leader Craig Williams with a winning double but also copping a suspension and losing a race on protest.

Melbourne's leading apprentice, Mertens has drawn to within four wins of Williams in the overall Melbourne jockeys' premiership after notching his 50th metropolitan win for the season when bringing up his second winner on Saturday.

Both wins came for the Lindsay Park team aboard Boom Time and Miss Gunpowder.

But Mertens was also first across the line in the opening race on Quilate only to lose the race on protest and also cop a suspension.

Mertens shifted out over the final 200m on Quilate and stewards ruled his shifting cost Ma Jones victory and reversed the placings after Ma Jones' rider Ben Allen fired in a protest.

Stewards later suspended Mertens for eight meetings meaning he will miss one metropolitan fixture, next Saturday at Caulfield.

His ban is due to begin after Tuesday and he can return at Flemington on April 25.