These hands are from Soledad Club, October 1, 2018.
Hand #8 was a duel between declarer and the defense.
West: ♠104 ♥AK72 ♦J2 ♣AK984
East: ♠KJ86 ♥QJ103 ♦K6 ♣1065
West opened 1♣—not liking two doubletons for NT and discounting the ♦J2 of diamonds—a good judgment. North passed. East responded 1♥ and South doubled for the other two suits. West raised to 2♥ and East, despite 10 HCP, correctly discounted his ♦K6 of diamonds on the auction and passed.
The lead was the ♥9. Declarer should recognize that RHO (North) is the dangerous hand. North can play a diamond to finesse Declarer's King. (You expect the ♦AQ to be behind your ♦K based on RHO's double.) You also expect RHO to have the ♠A. So, the only suit in which RHO MIGHT be able to get the lead will be in clubs. Yet clubs is the suit you must, eventually, set up as a source of tricks.
Plan A is to work on the spades. Take the heart in your hand and play another heart to Dummy's ♥K. Do not yet play the third round of hearts. You want to take the third round of hearts in YOUR hand as that will be your late entry after you have developed a spade trick so that you can discard one of Dummy's losing diamonds on a good spade. [At our table, Declarer erred by playing a third round of trumps before playing the spades.] Play the ♠10 and let it ride. LHO will win the ♠Q and shift to a low club—trying to get partner in to put that diamond on the table.
Take the ♣A and play a spade to your ♠J. South will take the ♠A (promoting your ♠K). South, however, will now play the ♣Q—still trying to get partner in. You have a counter to that: DUCK the ♣Q. [If Declarer had not already pulled that third round of hearts, he could have taken the ♣A and returned to his hand with a heart to discard TWO diamonds on his ♠K and the ♠8 when the ♠9 falls third round from the North.]
Once Declarer ducked the ♣Q, poor South has no choice but to cash her ♦A because she know the clubs are setting up for discards and that Declarer had winning spade(s) on which to discard Dummy's diamond(s).
So, careful avoidance play allows Declarer to take nine tricks. Many pairs were bidding 4♥ and going down one or two tricks.
West: ♠AK63 ♥QJ ♦A8432 ♣92
East: ♠Q105 ♥AK54 ♦65 ♣AKJ10
East usually played 3NT after the uncontested auction 1♦ (West) 1♥; 1♠ 2♣ (Fourth Suit Forcing); 2♦ 3NT. A black suit lead gives Declarer an easy eleventh trick. But suppose South leads a “top of nothing” heart. (If North had anything other than her diamonds, she could make the lead-directing double of 3NT which asks for the first bid suit of Dummy, but she does not have sufficient values for that.)
The club situation is a card combination everyone should learn. In many similar cases, Declarer should cash ONE high honor before finessing for the Queen, but that is incorrect when the holding is AKJ10 opposite two small. With that combination, an immediate (first round) finesse is correct but it allows a successful finesse to be repeated. This allows you to win FOUR tricks when the Queen is onside—even if that defender has Qxxx(x) or longer. Cashing the Ace or King first would limit you to three tricks when the Queen has three or more cards with it.
Since Declarer has 3 top spades, 4 top hearts (once you unblock them), 1 top diamond, and four clubs with the finesse, that is 12 tricks.
Deep Finesse shows 13 tricks with a double-dummy play in the spade suit, by playing RHO for the ♠98 doubleton. You play the ♠10 and South must cover or you let in ride double dummy. After the ♠10, ♠J and ♠A on Dummy, the ♠8 falls from RHO. Now the ♠3 to the ♠Q picks up RHO's ♠9, leaving the ♠K6 over LHO's finessable ♠74.
Such double-dummy plays can only be made when you see all four hands, so it is important not to beat yourself up about hands where Deep Finesse says you can make 13 tricks, but normal play makes only 12!
Incidentally the correct way to play the spade suit in isolation is to play three top rounds, hoping the ♠J falls which is a 55% chance, the sum of 35.52% (3-3 split + 16.14% (jack doubleton) and 2.42% (stiff jack). This slightly better than cashing the ♠A and then finessing the ♠10, at 51% = 50% + 1.21% for the stiff offside ♠J. The two lines are close enough however, that even a small chance of the spade length being in front of the ♠Q10 tenace tips the balance in favor of the finesse. Even a difference of one vacant space is enough. For example if in counting out the rest of the hand, you realize RHO has six cards that could be spades while LHO only has five cards, you should finesse.
Also even when the drop is favored, start with the ♠A or ♠K rather than the ♠Q to preserve the ♠Q10 tenace to cater to the rare void behind the tenace where a marked finesse is mandated.