"Then at Flemington in the Turnbull he demolished the second favourite Jameka so his record on these flat, big tracks speaks for itself."
McDonald also dismissed suggestions Hartnell might have already peaked earlier this spring.
"Hartnell certainly hasn't gone backwards," the jockey replied.
"I can't say he has improved as his form has been sensational so it is hard to improve off that.
"But I looked at him the other morning, he was bouncing and is a happy horse."
The John O'Shea-trained Hartnell remains the $5.50 favourite with TAB Fixed Odds to win the Melbourne Cup despite being thrashed eight lengths by champion mare Winx in the Cox Plate last start.
McDonald maintains Hartnell simply did not handle the tight Moonee Valley track in that race.
"He has never hung in his life but he was hanging at Moonee Valley, and he never got around that final bend," the jockey revealed.
"I thought he was going to run fourth or fifth but he once he balanced up in the straight he finished strongly for second.
"Winx was off and gone but I thought there was merit in his run."
McDonald, who's best Melbourne Cup finish was a second on Fiorente in 2012, said the barrier draw has been kind to Hartnell who is drawn to start out of gate 12.
"I'm happy with that," he said. "The horse jumps well and should be able to position up there in the race.
"With the (expected fast) tempo we should be able to slot in somewhere and if he relaxes, the will be hard to bowl over."
McDonald also warned punters not to read anything into Hartnell's struggling effort in the Melbourne Cup last year.
Hartnell drew wide so McDonald decided to ride the gelding back in the field only for the farcical race tempo to ruin his winning chances.
McDonald also pointed out that Hartnell's form and racing manners are vastly superior this spring.
