A stirring second-half fightback proved in vain for Hull who overturned a 10-point deficit to take a 12-10 lead midway through the second half before succumbing to three late tries.

However, Hull coach Agar was able to take much heart from a spirited performance by a makeshift line-up which was again missing a fit and healthy half-back in the absence of the perennially injured Adam Dykes.

"We know now that we can compete on the big day against the good teams," said Agar. "It was there for all to see that we are lacking in certain areas and have makeshift players at half-back. We also need to be a little bit smarter at times.

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"We know we can make it to these occasions – this is our third final in four years and there is no reason why we can't come back again.

"We have to remember what happened today, remember how we feel and know we can't be happy with a brave effort.

"Next time we get to a final, be it the Challenge Cup or a grand final, we want to win the game."

Saints scored two tries before the interval and had two others disallowed but Agar said he felt Hull were unlucky to be 10-0 down.

"I am sure Todd Byrne knocked on in the field of play which to my reckoning should have been a scrum or a handover and not a 20-metre restart," he said.

"I might be wrong but I do know that 10 seconds later Francis Meli put the ball down for a try. I also know there was a forward pass by Jon Wilkin before Matt Gidley's try.

"I am not hiding behind that. I think when you are playing games like this you have to catch the ball under pressure and on occasions we didn't do that.

"We gave it everything we have got. I thought we showed tremendous commitment to each other.

"With 14 minutes left I thought we put ourselves in with a shout after a couple of things hadn't gone our way.

"The effort to come back and haul ourselves back into that position showed a lot of character."

After edging into the lead for the first time with Kirk Yeaman's second try on 62 minutes, Hull made two errors with a knock on and a charge down which St Helens punished on each occasion to score tries that effectively secured them the Cup for a third successive season.

"I think we needed to hold on to the lead for more than a few minutes," conceded Agar. "We needed to try and hang on to the lead for six, seven or eight minutes and try and get them playing away from what they were working towards.

"A penalty late in the count and a dropped ball meant that never happened. The contrast is they are a team who can handle pressure situations a little bit better than most others in the competition."

Agar said he had taken the decision to omit Dykes and call up Richard Horne for his first match in five months following consultation with the club's physiotherapist and strength and conditioning coach.

Dykes broke down in training last Wednesday and with lingering doubts over his long-running knee injury and a thigh problem, Agar opted to go with Tommy Lee at scrum-half with Horne on the bench.

Horne stayed on until the end after replacing Lee Radford after 17 minutes, a longer stint than Agar had expected from a player who remains a stone under-weight following a serious neck injury which prevented him from training.

"We were going to see how it went with Richard," said Agar. "We anticipated getting two 25-minute periods and felt that if we were getting possession down their end we needed to make the most of it because you don't get many opportunities against St Helens.

"In three or four sets that we had in the Saints half early on we didn't put on what we practised and didn't give our strike players enough of a chance by attacking from the right areas.

"We put Richard on to give us a little bit of guidance in that area. I thought his effort given what he's gone through was enormous.

"We all saw how under-weight he is and in the end his fatigue cost us a little bit right at the end. By that point we'd lost Tom Briscoe and chances to rotate players in those areas so Richard had to do it even tougher."

Briscoe, 18, will have an MRI scan early this week to ascertain the seriousness of his injury, which was initially diagnosed as a fractured tibia.

Dykes, 31, meanwhile, will have a knee scan tomorrow and is resigned to having minor surgery to keep alive his slim chances of prolonging his playing career.

"I want to get it fixed," said Dykes. "It happened in the first trial game of the year back in February.

"It's been a tough year. I haven't trained because of it.

"In hindsight, I probably should have got it fixed in February but I battled on and it caused a few other injuries."

St Helens coach Daniel Anderson said he was a worried man when Hull came roaring back but paid tribute to his team's professionalism as they extended their winning run to 21 matches.

"We almost found a way to lose,"he said. "I thought we squandered ample opportunities in the first half, we had genuine try-scoring plays. I had a real bad feeling at the start of the second half, I thought it was going to come back to bite us.

"We are a very good front-running team but I knew the first try would provide momentum for Hull.

"Credit to us. We were honest for 80 minutes and I think that got us through.

"It was a tough game, I don't think people realise how much the first half took out of us."