Watch a full replay of how the six-year-old defied top weight in the feature at Exeter on Tuesday plus reaction from a delighted Daryl Jacob.
Thoroughly consistent last season since joining Henderson from France, the six-year-old had nevertheless failed to get his head in front.
He finished second at the Cheltenham Festival to Siruh Du Lac, was then fourth over the National fences at Aintree in the Topham – and was sent off the 5-2 favourite to make a winning return.
Giving 4lb and more to some classy rivals, he handled the drop in trip with ease – and Daryl Jacob always looked comfortable.
Harry Skelton attempted to nick a few lengths coming off the home bend on Destrier – but at the third last, Janika met it spot on and landed in front, gaining an advantage he would not relinquish.
Henderson was winning the race for the first time since the last of Travado’s three successes in 1995.
Janika beat the staying-on Dolos by two and a quarter lengths, with Destrier third and a break back to Lalor in fourth – who kept on all too late, having been outpaced.
Janika is now a best-priced 16-1 for the Ryanair Chase at the Cheltenham Festival, having been as big as 25-1 beforehand.
Jacob said: "He deserved that really. He ran some mighty races in defeat last season, and that is no more than the horse deserves.
"We are delighted because we needed to learn a little bit more about the horse, his grade and what we need to aim him at - so today was perfect for him.
"(The trip) was a little bit of a question mark, because he has been running over two and a half and two-five, but they went a nice even gallop there.
"The ground was still quick enough for him, so softer ground again will suit him better. Soft ground, two-one or two-miles-two round here is fine, but you probably wouldn't go two miles around a flat track.
"He is only a young horse, so he could have improvement in him. He has got a big heart - but he is only a small horse. A lot of credit has to go to Hannah (Ryan), who looks after him - she has done a wonderful job."
Paul Nicholls said of Dolos: "I'm thrilled with him. He went up five or six pounds for winning at Kempton and he has been beaten by just over two lengths, so that probably didn't help him.
"He has run a super race and is an improving horse. He is one of those horses that gives everything - he always performs above his capability, and he is genuine.
"He might be better off if we chucked him in some better races rather than carrying big weights in handicaps. We will find something for him. You don't mind horses like him that give everything."
Dan Skelton said of Destrier: "It was a good run. We were bang up there the whole way. He made a bit of a mistake four out, but he kept on galloping.
"There are no excuses. He has jumped exceptionally well apart from one jump, but that is how it is. It may have cost us a little bit, but I'm not grumbling."
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