Valerie Berlin and Jonathan Rosen's firm surged from the No. 29 slot in 2017.
Peter Finn's Finn Partners also recorded an impressive performance on the Observer list, claiming the No. 3 slot after being shut out from the Top 50 last year.
Compiled by Michael Kaminer, the Observer's list is based on what it considers "influence," rather than revenues, headcount or amount of awards won.
The Lede Co., PMK-BMC, DKC, Ketchum, HL Group, Global Strategy Group and M18 round out this year's Top 10 List.
The Door, (now No. 11), 42West (No. 13), Kekst, Rubenstein (No. 20) and Hiltzik Strategies tumbled from the 2017 Top Ten list.