Owner JP McManus landed a notable one-two after the 9-1 chance produced a gutsy performance to win by a neck from My Tent Or Yours, who had . The Ruby Walsh-ridden 11-4 favourite Hurricane Fly - the winner in 2011 and 2013 - finished fourth, behind The New One. However, the race was overshadowed by the death of Our Conor, who suffered a fatal injury in a heavy fall.
Jezki's victory means McManus is now the most successful owner in the history of the Champion Hurdle with five wins. "I am ecstatic about having the winner and the second," he said. "It means an awful lot to me.
"For me, the National Hunt season is centred around the Champion Hurdle because I didn't have many Gold Cup horses and I am unlikely to win the Grand National.
"It was all about the Champion Hurdle and full marks to Nicky [Henderson], Jessie [Harrington] and Eddie Harty who had the horses looking in mint condition today, as all the other runners were. It was a credit to everybody and it's just a very special day."
Geraghty, 34, who is now unbeaten in five outings on Jezki, said: "He's a great little horse. He had good form and he didn't have a lot to find with the best of them. I don't think his price reflected his chance.
"It was also a great run by the runner-up. I'm sure JP will be delighted with the first two home. The runner-up was getting to me, I needed the line."
There was more success for Ireland when Walsh, from County Kildare, rode the Willie Mullins-trained Vautour to victory in the opening race of the Festival, the Sky Bet Supreme Novices' Hurdle.
The duo scored a double when the 8-11 favourite Quevega extended her record by winning the Mares' Hurdle for the sixth successive year.
Mullins said: "She's a superstar. I'm so pleased for her and her connections, she has her own place in history now here."
Quevega's win meant Walsh has now ridden 40 Cheltenham victories consolidating his position as the Festival's most successful jockey.
The Irish have always been an integral part of the prestigious National Hunt Festival in which the best of Britain and Ireland's thoroughbred horses are pitted against each other in a way that is like no other meeting in the racing calendar.
Around 15,000 Irish racegoers attend the four-day meeting each day, almost equally divided between expats living in the UK and visitors from crossing the Irish Sea.
Star-spotting can be a full-time occupation, with many celebrity race fans making the trip, including a plethora of royals, actors and sporting figures.
Among those enjoying the racing were yesterday were Zara Phillips and Mike Tindall; the Olympic gold medal winner Dame Kelly Holmes; model Katie Price and her husband Kieran Hayler; and Premier League footballers including Swansea City's Jonathan De Guzman and Michel Vorm. Also spotted at the racecourse was former England footballer David Platt.
More than 200,000 pints of Guinness are expected to be drunk at Prestbury Park as around 235,000 people attend over the four days of the Festival. Punters are expected to wager £250m during the week.
The second day of the festival is traditionally Ladies Day when female racegoers don their most stylish and glamorous outfits.
As well as prizes for the racing, there are awards for best-dressed lady, best accessories and best hat, and an array of flamboyant head-pieces, feathers and fascinators will be on show. Other highlights of the week include the Queen Mother Champion Chase tomorrow, in which Sire De Grugy is favourite in the absence of racing's top-rated steeplechaser Sprinter Sacre.
The meeting builds up to the Gold Cup on Friday, 50 years on from the first of three triumphs in the race for the legendary Irish steeplechaser Arkle.
The weather is expected to remain dry for the rest of the week, according to the clerk of the course, Simon Claisse. "We have been jolly lucky as 12 months ago we were standing here on frost covers. It was more than 10C colder and we were wondering if the ground would come right," he said.
"It has been a mild but very wet winter. As we all remember, we had some very testing ground for the two race days here in January. But we expect the ground to dry out during the week as there is no rain forecast. Temperatures are forecast to rise, reaching 15C (59F) on Friday."
A record crowd attended the opening day with 57,098 - 814 more than last year - passing through the turnstiles.