Big Zeb reversed Cheltenham placings with Sizing Europe to land the Boylesports.com Champion Chase on the opening day of the Punchestown Festival.
The latter finished five lengths to the good at Prestbury Park in the Queen Mother Champion Chase, but Colm Murphy's runner turned around that form under Barry Geraghty.
The pair were neck and neck at the last and despite 11-8 favourite Sizing Europe rallying gamely, Big Zeb (9-4) got the verdict by three-quarters of a length.
Henry de Bromhead was evidently keen to ensure a good early pace for Sizing Europe as stablemate Changing Course set a strong gallop.
Changing Course could not keep up the momentum for long, though, and Sizing Europe jumped to the front at the fourth with Timmy Murphy happy to take control.
However, Geraghty was stalking him in behind and after Captain Cee Bee put paid to his chances with an untidy jump at the third-last, the big two settled down to battle it out.
They were side by side at the last but Big Zeb seemed to find an extra gear on the level - despite the fact Geraghty dropped his whip - and edged ahead.
Sizing Europe gave his all in trying to regain the lead, but Big Zeb proved too determined.
'That was fantastic. I'm delighted for him,' said winning trainer Murphy.
'Everything has gone right since Cheltenham and it was especially nice to win here. He's one in a million, he gives everything.
'I was happy all the way round and I thought Sizing Europe never looked as happy today as he did at Cheltenham.'
Geraghty said: 'I suppose the spring ground here is that bit fresher and it just helped my fella - he travelled better and jumped better.
'I was always able to sit comfortably behind Timmy but at Cheltenham I couldn't.
'We made a mistake four out and I thought that might knock him back but he was soon on the bridle again.
'He's good and he's gutsy. He's willing to take a chance and Sizing Europe is the same - they don't back off looking for an easy time.'