Made up of players under 25 from ASDA League One down, the Welsh team of amateurs took the lead in the first half against side using the tournament to warm-up for their vital World Cup qualifying showdown with the Czech Republic next month.
A try by Loughor fullback Andrew Banfield midway through the first half, converted by Bargoed outside half Jamie Howells, put the Welshmen 7-3 ahead in their historic first international after the Spaniards had taken an early lead with a penalty. Spain edged ahead 11-7 by the break and were expected to sprint clear in the second half.
Spanish Coach Ged Glynn had had his World Cup squad together for five days in Belgium prior to the game and started with only eight of his top line-up missing.
Some heroic Welsh defence restricted the Spaniards to two more tries after the break, one shortly after Caerphilly hooker Peter Harrison had been sent to the sin-bin, and Lott's men created three or four good scoring chances only to see the ball dropped close to the line.
"As a first game it was an excellent performance. The players really rose to the occasion and did their country proud," said the Welsh Clubs XV Head Coach Gerry Roberts.
"The Spaniards were a national team with vast experience and everything to play for. They dominated at forward with their big men, but we never took a backward step.
"What ball we won we moved around the field and caused them huge problems. We used typical Welsh flair behind the scrum and they had little or no answer to it.
"The players get a second chance on Saturday, when they play the losers from the game between Belgium and the French Amateurs, and the boys can't wait for another chance to represent their country."
The Spaniards' driving line-out, coached by former Aberavon Director of Rugby Chris O'Callaghan, caused Wales a lot of damage, but Lott's side earned huge respect from their opponents for their tenacity and adventure.
"It was a gutsy and committed performance from the Welsh side - everything we would have expected from them," said Spanish Forwards Coach O'Callaghan.
"They moved the ball superbly well and the centre Darren Humphries and wing Gavin Close caused us real grief. Those two boys would walk into any of the Principality Premiership sides back home and are probably talented enough to play with the regional sides.
"The Borders coach Steve Bates was at the game and I know he was making notes on one or two players. He, like myself, was very impressed at the way the Welsh players approached the game.
"They were technically sound, defensively very organised and committed and they certainly made the most of their possession. This is a great new stepping stone for players in Wales and I can see the Welsh Clubs XV doing very well in the future against the French Amateurs and English Counties sides.
"I'm sure the Welsh Premiership and Regional coaches will be taking a long, hard look at these players in matches like this and there is certainly a wealth of talent on display. This team will give players who won honours at under 16, 18 or 19 levels in the past, but missed on on professional contracts or places in the academies, another chance to get back into the semi-pro or pro system."
Welsh Clubs XV:
Andrew Banfield (Loughor)
Matthew Jacobs (Llangennech)
Darren Humphries (Bargoed)
Peter Smriglia (Loughor)
Gavin Close (Rhydyfelin)
Jamie Howells (Bargoed)
Rhodri Jones (Garndiffaith)
Ross Jones (Bargoed)
Mark Jones (Pontyberem)
Anthony Lott (Bargoed, Captain)
Jamie Noble (Pontypool)
Gareth Gore (Carmarthen Quins)
Celt Thomas (Whitland)
Andrew Packer (Newport Saracens)
Rob Downes (Beddau)
Gavin Hooper (Seven Sisters) for Rhodri Jones
Aled Davies (Whitland) for Smriglia
Owen Cotton (Ynysybwl) for Ross Jones
Peter Harrison (Caerphilly) for Mark Jones
James Bannister (Llanelli Wanderers) for Lott
Chris James (Narberth) for Noble
Lee Edwards (Tredegar) for Packer