Mercurial Lad lived up to the name in his past three starts, but the erratic gelding might finally be on the straight and narrow.

Thanks to several gear changes, Mercurial Lad produced a flawless run to win the TAB Highway Handicap (1200m) at Randwick.

Although Mercurial Lad went into Saturday's race after wins at Goulburn and Canberra, the galloper's inclination to wander off course gave co-trainers Paul Jones and his mother Barbara Joseph plenty to think about.

The addition of a pacifier and a one-eyed blinker did the trick and co-trainers Paul Jones and his mother Barbara Joseph had no concerns as Mercurial Lad ($4.40) beat War Hero ($5.50) by a length.

Jones admitted he had been mystified by the horse's behaviour on race day, given there was never an issue during trackwork.

"If he did it at home I could understand it. He's only done it on race days," Jones said.

"He seems to spot things in front of him and ducks away from them."

Canberra-based Jones said the next step for Mercurial Lad was undecided after he boosted his record to three wins from as many starts on heavy tracks.