Cryptic 9

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Across
  1. 3. virus found when plates and guests are halved.
  2. 4. suffocate through S&M alternative (7)
  3. 5. eventually within a marathon? (2,3,4,3)
  4. 8. be more savage and astound (8)
  5. 10. toilet in empty bed provides vital fluid (5)
  6. 11. shaking ill bear provides support for the blind (7)
  7. 13. first three friends took action without a conflict (8)
  8. 16. boiled ten white veg to retaliate (3,4,4)
  9. 17. shaved in confusion and disappeared (8)
  10. 18. recliner for a musician? (6)
  11. 20. insufficient space for a vegetable according to a drunk perhaps (3,4,4)
Down
  1. 1. keep doubly quiet and secret (4,4)
  2. 2. flood formed when first two destroyed sled (6)
  3. 6. misplace vital organ and despair (4,5)
  4. 7. wretch lived in disorder (5)
  5. 9. threadbare, but put on to wear away from home (4,3)
  6. 12. a non-medicinal pill put next to an unpleasant smell (7)
  7. 14. a group of words, I hear, describes a cat's primary weapon (6)
  8. 15. Chile stray is dishevelled and hilarious (10)
  9. 19. expand good fight (4)