The eagerness of Hugh Bowman to lock in a ride on a horse rated a borderline chance to make the field has raised trainer Matthew Smith's hopes of a Scone Guineas upset.

Smith revealed Bowman accepted a booking for Charlie Who despite uncertainty about the three-year-old getting into the richest race of the two-day Scone Cup carnival

"When he took the ride I thought my horse must be a shoo-in to get a run because Hugh probably had the offer of a lot of nice horses in the race," Smith said.

Bowman's foresight was rewarded when Charlie Who scraped into the field for the $400,000 race on Saturday and Smith had only more good news for the leading jockey as the finishing touches were put on the horse's Guineas preparation.

"On his work during the week he'll definitely be competitive in it," Smith said.

Charlie Who is the least experienced Guineas runner with three visits to the races returning two wins at Goulburn before a last-start defeat at Wyong.

But he will go into the Guineas as one of the best-supported horses alongside the favourite Sure And Fast after firming from $21 to $14.

Charlie Who will start from the outside alley in the 16-horse field and the barrier confirms Smith's plan to have him ridden from behind.

"He got a bit of a shock when we rode him near the lead at Wyong. He didn't know much about it," Smith said.

"On a bigger track at Scone I think he's definitely better smothered up and having one crack at them late."

Gai Waterhouse rates Nayeli, a $10 Guineas chance, among the best of the six Scone runners she will send around on Saturday.

Waterhouse landed the Guineas trifecta last year when Cosmic Endeavour led home Liberty's Choice and Ryker and a recent barrier trial win points to Nayeli being a sharp improver on two sub-standard Sydney autumn carnival runs after a first-up win in the Fireball Stakes.

One of five fillies in the race, Nayeli defeated Wandjina in a Randwick trial last week after making most of the running to comfortably hold her Royal Ascot-bound stablemate.