The given auction took place when this deal was originally played. 3NT was not a very good bid by South. It wrong-sides the contract if North has the ♥Q or even the ♥J. North's 4♣ bid was also atypical, as since South has shown at least a double stopper in hearts, bidding over 3NT should show slam interest (which was clearly not the case here). Anyway, the final contract is a sound one. Your task here is to make the contract after West leads the ♠4 (East-West play fourth-best leads).

Solution:
You have certain losers, one each in hearts and clubs. Therefore, you need to hope that the diamond finesse is onside. It also looks as if West should have the ♠K, as the lead of a low card usually suggests an honor in the suit. While this inference is reasonable, it is not foolproof. West may have made a count card lead, or he might be holding the jack and possibly decided to consider it as an honor.

You need to rely on the diamond finesse, but you don't need West to have the ♠K as well. The correct play is to go up with the ♠A at trick one. You then play a club to the ace, take a diamond finesse, play a club to the king and take another diamond finesse. All has gone well so far, and you play the ♦A and discard your spade loser, and until an opponent ruffs in with his master club you will simply keep playing diamonds.

This deal was not too complex, but illustrates the importance of taking your time at trick one, for the natural looking play of running the spade lead to the queen would have failed on the lie of the cards. And yes, 3NT is much easier to play since the diamond finesse is working.

Analysis:
Bridge Baron's double dummy solver confirms of course that going up with the ♠A and playing to dispose the spade loser at the first opportunity is required to make the contract.

Bridge Baron's Line of Play
Bridge Baron finds the winning line of play on this deal, making the key play of the ♠A at trick one. Bridge Baron has an advantage over humans in that it cannot be lulled into making a seemingly "natural" or "intuitive" play.
Par Contract Analysis:
The par contract on this deal is 5NT by North-South.

Bridge Baron deal No : N4074-83365-11413-17808-62698-56370