La Bague Au Roi made a fine start to life over the larger obstacles with victory in the KKA-Highpoint Beginners' Chase at Newbury.
Rated 150 over hurdles following a good campaign last term which included three wins and solid efforts in defeat at the Cheltenham and Punchestown Festivals in the spring, the mare took to fences like a natural in the hands of champion jockey Richard Johnson.
The pair stalked front-running market rival Lostintranslation for much of the extended two and three-quarter-mile contest before taking it up after the second last.
Lostintranslation stuck to his task well in defeat but a swift jump at the last all but sealed victory for La Bague Au Roi, who powered home to score by a length and a half despite appearing to idle slightly on the run-in.
Greatrex said of the 15/8 winner: "When we went to bed last night, we couldn't have imagined it going much better than it did on the day.
"Richard was really pleased with her and she jumped well. He said there's no rush to step her up any further in trip and it's great to just get the first one out of the way.
"There are plenty of options now we've beaten the boys as the mares' programme is there for us if we want but I'd imagine she'd scare plenty of them off.
"She was entitled to do what she did today based on hurdle ratings and she's always been good when fresh - there's a lot to look forward to. Something like the Kauto Star Novices' Chase could come under consideration, we'll have to see."
Nicky Henderson recorded a double earlier on the card with French Crusader (5/1) winning the opening Fuller's Conditional Jockeys' Handicap Hurdle under Ned Curtis and the Jeremiah McGrath-ridden Lust For Glory taking the CSP Mares' Novices' Hurdle at 9/2.
Henderson said: "She was in all sorts of mares' maidens last week though we got brave, but it is only a novice hurdle just a £20,000 one. We will have to go upstairs now. She is one of the better mares you will see."
On French Crusader he added: "He is in at Sandown on Sunday and you would have to think about it as I don't know what they will do with him and he will have no penalty."
David Maxwell enjoyed a winner in his own colours aboard the Philip Hobbs-trained Ecu De La Noverie as the 33/1 shot saw off 13/8 favourite Mister Fisher in the Agetur UK Novices' Hurdle, while the Pertemps Network Handicap Hurdle went to Jersey Ben (9/1) for Oliver Sherwood.
Sherwood said: "He is a cracking little horse and Tony Taylor his owner lives in Jersey, hence why he is called Jersey Bean.
"He only won one novice last season, but he got an infection in his hind leg. He is going the right way now."
Nick Williams and Lizzie Kelly teamed up for success in the Dawnus Handicap Chase with Siruh Du Lac justifying good market support to score by a length and three-quarters from Chef D'Equipe at odds of 7/1.
Kelly told Racing UK: "He's a very good jumper and it's exactly what he's good at racing around here.
"He was having his first run and he's quite big so it's been touch and go getting him properly ready. He's been keen in the past so I wanted to get a good spot and with him, his main asset in his jumping so you may as well go for it. That's where he makes up most of his ground.
"Every question we've asked of him he's answered which is a good sign for such a young horse. He's willing, has a great attitude and I don't think he'll ever win a race looking like the next best thing, but it's not a bad thing that he looks after himself a bit.
"He's come into his first race and won well so you've got to be looking for him to go quite far this year."