Sent out the $1.60 favourite under regular rider Opie Bosson, Imperatriz scored a long-head win over Private Eye ($5) with Espiona ($26) a half-length away third.
Trial watchers were concerned after Imperatriz was below her best at Cranbourne on February 5 when beaten out of a place.
Hot weather leading up to the trial was given as an excuse for the lacklustre performance, but trainer Mark Walker did not lose confidence in the mare.
That confidence was completely restored after Imperatriz galloped at Moonee Valley last week.
"Good horses, they probably save their best for race day," Walker said.
"It was a lacklustre trial, it really was, but when we galloped her last Monday, we were really happy with her."
Walker said he had not planned any further than Saturday's Lightning Stakes victory, wanting to see how Imperatriz returned after an unbeaten four run campaign last spring.
He said he would not be surprised if Imperatriz rose to another level.
"She's a gem, really, to do it in the spring and come back and win like that," Walker said.
"Full credit to the second horse. He's a really good horse and he stuck it to her today, so I think you saw two really good horses fight out an exciting finish."
"We'll just get her through today and see how she is and come up with a plan going forward."
Walker said he would fly back to New Zealand before returning later in the week where he and assistant-trainer Ben Gleeson would firm up further autumn plans for Imperatriz.
