ACROSS
1. <severe> STRICT = DI out of DISTRICT
4. <benediction> BLESSING = GLIBNESS*
10. UP SET = UPSET <underdog victory>
11. (ATTIC POET)* = PETTICOAT <historical undergarment>
12. (_T THEOREM FOGG_)* = FROM THE GET-GO <since day one>
15. IN SIP I'D = INSIPID <tasteless>
17. <you can get four-of-a-kind here> YAHTZEE = (YANGTZE, H←NG) _E
18. SUP outside EVEN = SEVEN-UP <soda>
20. D_ out of BEDTIMES = BETIMES <early>
21. IMPROV IE outside DE NC = IMPROVIDENCE <thoughtlessness>
25. <Italian meal> SPAGHETTI = S + P (AT EIGHT)*
26. R inside GIFT = GRIFT <con artistry>
27. (FLATUS IT)* = FLAUTIST <one tooting>
28. "SEIZE A" = CAESAR <general with imperial ambitions>

DOWN
1. <most tipsy> SQUIFFIEST = QUIFF inside SIEST_
2. PERSONS* + I'VE = RESPONSIVE <providing feedback>
3. CU + TI _T_ = CUT IT <suffice>
5. THE inside LILY = LITHELY <supply {supplely}>
6. <one makes rock career {move quickly}> SLINGSHOT = (HIT SONGS)* outside L
7/19. (IRONY outside P) RITES = IRON PYRITES <a deceptively-common mineral>
8. <one wearing black perhaps> GOTH = GOT H
9. APP END = APPEND <add on>
13. OZ ←MY← AND I AS = OZYMANDIAS <a vain tyrant>
14. <informer> NEWSLETTER = LET inside WESTERN*
16. PANAM AT outside A H = PANAMA HAT <boater>
20. <beef extract> BOVRIL = V R_ inside BOIL
22. DOG MA_ = DOGMA <teaching>
23. <no way> AS IF = ←(...f)F IS A(v...)←
24. H_ AKA = HAKA <ceremonial war challenge>