But after having staged three inspections during the morning, Exeter clerk of the course Barry Johnson issued a triumphant thumbs-up.
While Thornton did not find the winner's enclosure with his sole ride, the star rider was still the happiest man on the racecourse as he completed his miraculous return to the saddle.
Thornton was left in a heap on the Newton Abbot turf in July after a horrific fall from Hell's Bay, which left doctors predicting a year on the sidelines for the leading jockey. But Thornton has whittled down that absence to five months and he came close to making the perfect comeback on Causeway King in the Exeter Hurdle.
Trained by Thornton's manager, Alan King, the four-year-old made most of the running, only to be caught late on by rank outsider Salontyre (22-1), ridden by Isabel Tompsett.
"I'm delighted racing is on and it's great to be back," said Thornton. "I'm still having a little blow and there's no substitute to riding, but after two or three more rides I'll be spot-on. When I was told it would 12 months originally, I cried, so to get back in five to the day is brilliant."
Last season's Fred Winter scorer, Sanctuaire, was sent off the hot favourite but he could only finish third, having pulled for his head for much of the contest. The absence of likely hot favourite Royal Charm meant just two runners went to post for the Harry Dutfield Memorial Novices' Chase, but that did not stop the pair fighting out a thrilling finish.
Tarablaze was sent off the 4-11 favourite in a match against 2-1 shot Hidden Keel. The former made most under Tom O'Brien but he ran down a couple of fences in the straight to give Hidden Keel supporters real hope heading towards the final fence.
Hidden Keel and Paddy Brennan briefly hit the front on the run to the line, but Tarablaze fought back and had a length and three-quarters in hand passing the post.
Trainer Philip Hobbs said: "He was idling in front, and was never travelling that well - he also jumped a little bit left. Probably with a lead it wouldn't have been a problem."
Sponsors Coral chopped C'monthehammers to 40-1 for the Welsh National after Nigel Twiston-Davies' charge showed reservoirs of stamina in the gruelling Axminster Carpets Devon Marathon Handicap Chase.
Meanwhile, Ralph Beckett and Cast Of Stars left each other on the best possible terms with victory at Kempton on Saturday.For the gelding a hurdling career in Wales awaits, while Classic-winning trainer Beckett is about to relocate within Hampshire from Whitsbury to stables in Kimpton, Andover.
The 6-4 favourite has had a frustrating time of things on the level but was helped by a typically cool George Baker to lift the Best Odds Guaranteed At mobile.williamhill.com Maiden Stakes in tidy style.
"He is off to Evan Williams now, as the owner David Barrie has hurdlers with him," said Beckett. "That could well be our last runner from Whitsbury."
The weather is still hitting racecourses hard, though. Conditions have improved markedly over the last few days but Leicester have announced an 11am inspection today ahead of Wednesday's fixture, while today's Lingfield meeting is subject to a 6am inspection.
Yesterday's meeting at Warwick was abandoned because of frost. "We were above freezing all night and at 5.30am we were pretty confident," said clerk of the course Andrew Morris. "However, then we had freezing fog descend upon us."