The Tony and Lyn Prendergast-trained galloper fought determinedly for the narrowest of wins over North Island raider King Cougar in an exciting finish to the $35,000 feature.
Trudeau has banked more than $60,000 in six wins since being purchased by Lyn Prendergast for $5000 from an online auction site last year.
The 5yr-old gelding, who was syndicated for racing among a large group of owners, will race for just short of 24 times his purchase price in his next start thanks to his Oamaru Cup win.
''Lyn bought him off the Gavelhouse website for $5000. Murray Baker owned him up north,'' Tony Prendergast said.
''He had had 20 starts for three wins, three seconds, three thirds and three fourths.
Trudeau will not only bank the winner's slice of the $100,000 prize pool, but he will win a $60,000 bonus for his owners if he is able to win the group 3 Winter Cup at Riccarton.
The path to an agonisingly close Oamaru Cup win was a highly unusual one.
Trudea was not originally being aimed at the race until Lyn Prendergast put in a last-minute nomination.
The Prendergasts then went in search of a rider to take a booking on Trudeau at 56.5kg.
That turned out to be another slightly usual exercise.
''Chris Johnson was to ride him but there was a bit of a mishap and he was already booked to ride King Cougar,'' Tony Prendergast said.
''Jacob Lowry wasted like hell to try to ride him but he rang yesterday to tell us he couldn't do it.
''Then we switched to Jason Laking and he had a go and he couldn't do it.
''They were going to ride him 1kg overweight.''
Finding a jockey for Trudeau should have been a no-brainer as leading South Island rider Samantha Wynne shares in his ownership.
However, she has been forced on to the sidelines with complications from the horror knee injury that has had her out of action for much of the season.
Eventually, the Prendergasts secured the services of Wynne's good friend and fellow jockey, Tina Comignaghi.
Comignaghi claimed 1kg on Trudeau and that was the difference that resulted in Trudeau winning by a nose.
''We were going to be 1kg over, then when we put Tina on we were 1kg underweight,'' Tony Prendergast said.
Tony Prendergast paid tribute to his charge for the tenacity he showed under Comignaghi's urgings.
''He is really tough horse, he is so tough,'' the trainer said.
Less than a length separated the first five horses home in yesterday's feature.
Owen Patrick was half a head behind King Cougar in third placing. Forged and Elfee trailed them home.
The race result had little effect on the market for next month's Winter Cup.
Trudeau was rated at $18 and King Cougar was at $14 when the race market reopened after the Oamaru Cup.
North Island raider Rosewood remained favourite at $4.
The Central Districts galloper ran second behind the exciting Helena Baby in last weekend's Opunake Cup.
