Derbyshire's under-18 team manager John Briggs said it was the "strength of the depth" of his squad which earned them County Cup promotion.
He took a team of 10 players and used eight of them over three days at the AEGON 18U County Cup competition, in Loughborough, to top Group 4B.
Briggs said the level of tennis his squad displayed was "fantastic", as they beat teams from Avon, Durham and Cleveland and the East of Scotland.
After 26 matches, promotion was eventually decided in the final match of the tournament, with doubles partners Jacob East and Curtis Clarke clinching the win on a match tie-break.
Briggs, who was accompanied by team coach Ashley Broomhead, said the boys thoroughly deserved the success.
He said: "The lads played as a unit for three days and their success came because they worked as a team, rather than individually.
"It can only make them better tennis players and people and it was very satisfying for me to be a part of their hard work. I was overjoyed when they were promoted.
"Every year, you go to the County Cup with the intention of staying in the group but, this year, after a day or two, you felt like there might be something more.
"But I did know it would be extremely tight and it did go down to the wire on the final day. It's fortunate it went to us and I'm so pleased we came over the final hurdle.
"It's particularly good for Derbyshire tennis because, given the age of most of the boys, they should be available next year, which is promising for 2013."
Briggs' team comprised Thomas Bywater, Curtis Clarke, Jay Clarke, East, Mark Eastall, Sam Ferguson, Daniel Lea, Jamie Praditngam, James Riley and Mandeep Singh Sangha.
Matches were the best of nine rubbers, with six singles and three doubles.
The team finishing top of the division were promoted for next year's competition, while the side with the fewest points were relegated.
Derbyshire opened their account by beating Durham and Cleveland 6-3 on the first day of the round-robin tournament, at the Dan Maskell Tennis Centre.
Singles wins came from Lea, Curtis Clarke, Jay Clarke and Ferguson, before both Jay Clarke and Ferguson and Curtis Clarke and East teamed up to triumph in their doubles.
This set them up for a second-day showdown with Avon, who had lost the previous day to the East of Scotland.
Their 7-2 victory came after Riley, both Clarke brothers and Praditngam won their singles rubbers and the squad won all three of their doubles matches.
Briggs added: "There was a bit of chopping and changing of the squad.
"What I think clinched it for us was the strength in depth in the squad."
On the final day, Derbyshire played the East of Scotland in a straight promotion fight, while Avon and Durham and Cleveland clashed to avoid relegation, with the latter losing 5-1.
Wins from Sangha, Praditngam and Curtis Clarke saw Derbyshire take a 3-0 lead but East of Scotland levelled after winning the top-three ranked matches.
Sangha and Praditngam then won their doubles match but Riley and Lea lost theirs, before Curtis Clarke and East won 1-6, 7-6 (5), 1-0 (7) to claim Derbyshire's 5-4 win and promotion.
Courtesy of Derby Telegraph