An old partnership will be revived on Saturday when Guy Walter legs Robert Thompson aboard Kobi Sun in the Lord Mayor's Cup at Rosehill.

Since Thompson rode Walter's first Group One winner almost 20 years ago both jockey and trainer have come a long way.

Thompson established a national riding record in 2008 and last weekend became the first Australian jockey to post 4000 winners.

Walter had only had Sharscay in his stable for a matter of weeks when the horse won the 1995 Canterbury Guineas under Thompson but has become recognised as one of the country's leading horsemen.

He has prepared a steady stream of top-line gallopers headed by 13-time Group One winner Tie The Knot with Spinning Hill, Defier and Appearance among his other stars.

Kobi Sun is lightly raced but has shown enough to prompt Walter to put him in Saturday's Listed race against seasoned stayers and the trainer hopes he can perform well for Thompson.

"We are extra lucky to have Robert on him. Lucky he was riding at the meeting and lucky he was available," Walter said.

"Robert rode my first Group One winner and has ridden many, many winners for me since."

Thompson clocks up a lot of miles each week but his visits to Sydney nowadays are rare. He spends much of his time riding on the country and provincial circuit.

His other ride at Rosehill is Rebel Dancer for Port Macquarie trainer Jenny Graham in the 1100-metre race for fillies and mares.

Kobi Sun is among the outsiders in the Lord Mayor's Cup and comes to the race off a pleasing fourth over 1600 metres at Warwick Farm on Anzac Day.

"I thought his last run was very, very good," Walter said.

"The mile was way too short for him.

"He hasn't had a lot of racing but from what I've seen he is a promising stayer.

"He has to take a step up in grade and the 2000 metres may still be too short against this opposition but I think he can run well."

Walter is confident Kobi Sun's stablemate Dream Folk can acquit himself well in the 1500-metre benchmark 75 as long as the rain stays away.

The four-year-old has struggled on rain-affected tracks in his first two runs this campaign.

The winner of five of his 13 starts, Dream Folk is by Dream Ballad, a stakes-winning half brother of Tie The Knot.