These two hands are from Soledad Club, September 3, 2018.
South (Pro): ♠A ♥753 ♦3 ♣AKQ87652
North (You): ♠K1083 ♥9864 ♦K542 ♣4
You are playing with a professional bridge player. West, on your right, opens 1♦ and you pass. East bids 1♠ and partner passes. West bids 1NT and you pass. East bids 2♥ (this limits his hand, because good hands go through New Minor Forcing, i.e. 2♣ on this sequence) so he is showing at least five spades and four hearts and fewer than 10 good HCP. At this point, partner bids 3♣. West bids 3♠ and you pass. East passes and partner bids 3NT. No, partner has NOT gone crazy. You should expect partner to have a solid 7 or 8 card club suit and a stopper in one of the majors (probably spades as that is what they have agreed upon). He may have a heart stopper as well, but may not. He is clearly counting on you to have a diamond stopper. (You are marked for some points because both East and West have limited their hands). Partner probably expects you to come down with 6-8 HCP. West passes. You pass. East thinks a long time and bids 4♠. You are just SALIVATING to double this. Alas, partner—he later admits “from frustration” because he was sure he was making 3NT—bids 4NT. That goes down two, mercifully undoubled. 4♠ would have been down two, doubled.
My partner's bid was similar to the “Gambling 3NT” opening that some people play. He just figured from the auction that I had a diamond stopper, and hoped I had a heart stopper. If I had held ♥J10xx instead of ♥9864, he would have been a hero in 3NT. The full hand was:
North: ♠32 ♥QJ ♦AQJ5 ♣AQ642
South: ♠A ♥A83 ♦K97643 ♣KJ7
The current ACBL rules allow you to bid 1NT with a singleton, IF that singleton is an Ace, King or Queen. Just because you can does not mean you should! Partner elected to open the South hand 1NT. I had a classic Quantitative Raise with 16 HCP, so I bid 4NT and he passed with his 15 HCP. Unfortunately, we are cold for 7NT or 7 in either minor. If he opens his 6-card minor, I will bid 2♣ (game forcing). He will raise me to 3♣ and I will bid 3♦, saying I had diamond support all along. He can cue bid a heart control (3♥), and I'll show club control (4♣). He can then bid a spade control (4♠), and we will get to 6♦. (We probably will not get to NT, but at least we'll be in slam.) Getting to 7♦ is not reasonable, because I don't know about his sixth diamond, and he cannot be sure that my 2♣ bid shows five in the suit since I showed I had diamond support from the beginning. Two out of 13 pairs got to the minor slam.
A reminder of the Kantar Adjunct when partner makes a Quantitative Raise (from 1NT to 4NT). With 15 HCP, you pass. With 17 HCP, you bid 6NT. If you have 16 HCP that you like (more Aces and Kings than Queens and Jacks and NOT 4-3-3-3), you bid a 4-card (could be 5) minor. Since partner did NOT do Stayman or transfers, she does not have the majors, so the odds of finding a 4-4 minor fit are decent. If you find an 8-card fit, you can make slam even with only 31 or 32 HCP. Once you bid your minor, partner can play 5NT, bid 6NT (with 17 HCP, now knowing that you have 16), or bid 6 of the minor with a fit. This agreement gives you one more bite at the “slam” apple.