He was confident until the barrier draw, which gave him pause for thought before he decided to push on.
"She was in great shape but I didn't know if any of my three fillies were good enough, but they all ran as good as they could run," Weir said.
Carted into the race after settling last, jockey Craig Williams just found clear running and ran them down one by one.
Weir was certain the Wakeful Stakes over 2000 metres would be her next assignment but he wasn't so sure about whether the Oaks would be on the agenda.
Having now won four on the trot after breaking through at a Sale Maiden in September, she had trained well and matured.
Tom Dabernig, who trained the runner-up Fundamentalist, was disappointed but encouraged by the run.
"He did everything right. He followed smart melody, he hit the front... the winner came from last and did us right on the post," Dabernig said.
It didn't take long for Dabernig to echo the thoughts of fellow trainers when it came to the winner.
"I think it was just one of those things ... Weiry beat us again," Dabernig said.
Land of Plenty overcame a wide barrier draw to land back-to-back group one wins for the leading trainer.
Ridden from an outside barrier, the five-year-old sat with cover before unleashing a withering sprint to take the mile in decisive fashion.