A one-level response to an opening bid may be based on a four-card suit, so opener prefers four-card support to raise. Some systems
require it. But I advocate raising with good three-card support in a suitable hand. Auctions are easier when a trump fit is established quickly.
If you open one club on Q 8 7, K 8 7, A 10 7, A J 6 5 and partner responds one heart, bid 1NT. But if youopenon87,KQ6,A876,KQ 7 6 and hear one heart, a raise to two hearts is fine. You have three good hearts, prime values and a possible ruffing feature.
A three-card raise may let you reach a good contract on a 4-3 fit. In today’s deal, North judged to raise South’s one-spade response. South hadn’t responded in a red suit and would often have a fivecard spade suit.
After South leaped to four spades, West led the king of hearts. East won the second heart and shifted to the nine of diamonds, and South took the ace.
If South had continued with the three top trumps, he’d have gone down. (South couldn’t afford to concede the fourth trump, and if instead he started the clubs, East would ruff the fourth club, leaving South with a diamond loser.) But at the fourth trick, South played a low trump from both hands. He won the diamond return, drew trumps and ran the clubs for 10 tricks.
East’s best defense is to lead another heart at Trick Three, but South can still succeed. He discards a diamond, ruffs in dummy and takes the top trumps. He can then run the clubs to get rid of his last low diamond as East ruffs with his high trump.