And it was thrilling to see two men in direct contention for a single international place, going at it so wholeheartedly and, just as the script required, having such a decisive effect on the afternoon.
The contrast in styles could hardly have been more obvious. Andrew, calmly kicking a penalty in the first couple of minutes, had the air of slight remoteness that seems to characterise all thoroughbred fly-halves.
It is the gift of making time and space in the hurly-burly; but in this case, his critics say it is more like the result of an unwillingness to get involved in the work of attacking at close quarters. Barnes, on the other hand, looks like a man whose instinct is to get stuck in. Small, dark and square, he is built for burrowing, and you might think twice before trying to stop him.
In fact that's what Andrew did, in the first genuinely dramatic moment of the match, after five minutes, when he stopped Barnes in his tracks and an enthralled shudder went round the ground.
A minute or two later, when Barnes had a kick smothered by Micky Skinner, the South-West's captain appeared to be in for a troublesome afternoon.
It didn't seem much more promising at half-time, when London led by 14 points to 3 and Andrew, looking full of confidence, had kicked three penalties. Barnes called his men into a huddle and didn't let them go until the restart. Andrew, by contrast, let his men relax and have a drink before convening them for a brief conversation.
Both captains were receiving plenty of possession from their scrum-halves, but in the first half only Andrew had been able to turn it into anything meaningful, taking advantage of the space given him by Steve Bates's long pass to trigger a series of fluent passing movements. His harrying when Richard Hill fumbled the ball had set up the opportunity from which Alex Snow scored London's first try.
That was how the second period began, too, but gradually Barnes's persistence was rewarded, imperceptibly changing the shape of the game as the efforts of the South- West began to win him the initiative from a London side whose players, at 17-3 up, probably thought they had done enough.
The idea that it might all be going wrong for them occurred almost on the hour, when Andrew failed to tackle Nick Beal, speeding on a diagonal run for the right-hand corner flag. Beal's extreme effort took the South-West into the lead for the first time, and collective self-belief began to flow from Barnes into his men.
Before they could consolidate their advantage, though, Andrew snatched it back with a piece of initiative that made a mockery of those who call him a conservative tactician. Breaking around a scrum on the narrow side, he put his head down and weaved for the line, blowing the South-West's cover apart.
Seven minutes later, Barnes made his reply with a flashing break through the middle of the London defence on the edge of the 22, setting off a move that culminated in Jeremy Guscott's stylish touchdown in the left-hand corner.
With 10 minutes to go, and his side now trailing by a single point, Barnes ballooned an attempted drop-goal wide from a good position just inside the 22.
The match was now boiling, and five minutes later Andrew was powerless when Barnes hoisted a hopeful up-and-under, followed it up himself, and came out of the ruck like a pit-bull terrier with a lamb chop. Webb, whose boot had not had the best of days, lined up the resulting penalty with the air of a man who dared not miss, and didn't.
On the day, Barnes had won, but the match told us little that we didn't know. The statistics, which show roughly equal amounts of possession but a greater inclination on Andrew's part to let the ball out to his threequarters, do not reveal that Barnes received most of his passes from Hill while under pressure in his own half, with nothing much on.
If his touch-kicking was unsatisfactory, that may have owed something to the heavy conditions and the fact that the ball left the boot with all the alacrity of a bag of wet cement.
The success of Barnes's captaincy was, naturally, one of the features of the match. But that is hardly likely to be a relevant consideration when the England selectors choose their team to meet France in the first Five Nations' match next month.
HOW BARNES AND ANDREW COMPARED YESTERDAY
Possession in open play 26
(passes 19, kicked for touch 3, kicked for position 4)
Tries 1, Penalties: 3 (1 miss), Conversions: 1 (1 miss), Drop goals: 0
Possession in open play 27
(passes 11, kicked for touch 11, kicked for position 5)
Tries 0, Penalties: 0, Conversions: 0, Drop goals: 0 (1 miss)