Puzzle

 ACROSS

  1 Thanos, to the Avengers

  6 Staff opening?

 10 In the thick of

 14 "Later"

 15 Throw a hissy fit

 16 You can see right through it

 17 *Ingratiate yourself

 19 Sally who was the first U.S. woman in space

 20 Pavarotti solo

 21 Biological messenger letters

 22 Pickle juice

 24 Compadre

 25 Formerly named

 26 *Most direct route

 28 With 43-Down, home for Macron

 30 Ace or deuce

 31 Cube that's rolled

 32 Positive particle

 34 Harbor mammal

 35 *Teddy bear, for one

 39 Bengaluru bread

 40 Beach city near Los Angeles

 41 Road trip lodge

 42 Smartphone downloads

 44 Many Stonehenge celebrants

 48 *Snobbish

 50 EMT training component

 51 Dalmatian doc

 52 Judge's proceeding

 53 "___ Came in Through the Bathroom Window"

 54 Cheese in spanakopita

 55 Italian automaker

 56 Celebration's continuation, and a hint to the ends of the starred answers

 59 Baum princess

 60 Fancy hairdo

 61 Airline seat request

 62 Friendly email sign-off

 63 Fumbles, say

 64 "___ II" (2018 boxing movie)

DOWN

  1 "Room" or "key" preceder

  2 Kind of network in computer science

  3 A la King?

  4 Vidal's "___ Breckinridge"

  5 "I did it!"

  6 Whooping bird

  7 Hot rock

  8 A star may have a big one

  9 "Giant" author Edna

 10 4/

 11 Theme

 12 Refusing to face facts

 13 Sandra of "Gidget"

 18 Unencumbered by

 23 Ink color for debts

 25 Spongy toy brand

 26 Far from fresh

 27 Slippery as an ___

 29 Constructed, as a web

 30 Final musical passages

 33 Dangle a carrot in front of

 34 Too big for one's britches

 35 Disinfect

 36 Puzzles with seven pieces

 37 RCA Victor pooch

 38 Certain steel beam

 39 Medical research org.

 42 Word associated with a lightbulb

 43 See 28-Across

 45 Hardly inclined (to)

 46 Stinging plant

 47 Remained behind

 49 Try to punch

 50 Puck and Child

 53 Cake mix instruction

 54 County event

 55 Key ring item

 57 "___ he's a jolly good fellow ..."

 58 Ms. ___-Man

Solution