Neil Aspin admitted he was relieved after his side grabbed a late win over Maidstone United to book their place in the third round of the FA Trophy.
Seddon pounced in the dying seconds to set up a third round tie at home to Chelmsford City after an at times frustrating night at the Shay.
The frontman, who has now scored six goals in the competition this season, had earlier opened the scoring before United had pegged the Shaymen back.
Boss Aspin said he was pleased to have avoided a replay in Kent in January.
“I feel relieved because the thought of having to travel all the way down to Maidstone for a replay and to lose another league game when we’re already well behind is not really what you want, so I think a draw would certainly not have been a good result for us.”
Town dominated the opening exchanges and looked to be on course for a routine win until mid-way through the first half when the visitors levelled.
“I thought when we took the lead we were playing well and it looked a matter of time before we would go 2-0 up,” said Aspin.
“But after they equalised they looked the better team and they put us on the back foot. They had some lively players bringing the ball from midfield and they caused us problems but second half you would have to say on the balance of play we desevred to win the game.
“When you’re going into injury time you’re hopeful but you don’t expect it, and we had many chances before that to take the lead,” said Aspin on a night when Seddon, as well as Danny Lowe, Liam Needham and Lee Gregory all spurned good chances.
“To be fair to the players they kept plugging away and they did get some good deliveries in, particularly from the left, and if you keep doing that then you expect at some stage to get a goal. The players continued to push forward and it was lovely to see the goal go in at the end.”
On Seddon, Aspin added: “Gareth has worked really hard in the last few weeks and scoring that chance late on has sent everybody home happy.”