Qoraa sii wadida faqradan - 13 Sebtember 2018, Karlsson (oo ay weheliyaan Francis Perron) waxaa lagu beddelay San Jose Sharks si loogu beddelo Chris Tierney, Dylan DeMelo, Josh Norris, Rūdolfs Balcers, Sharks 'qoraalka koowaad ee doorashada ee 2020, doorashada wareega labaad ee 2019
iyo xulashada wareega labaad ee sanadka 2021. Wuxuu dhaliyay goolkiisii ugu horreeyay ee Sharks bishii Nofeembar 18 guushii 4-0 ee St. Louis Blues. Kadib bilowga xilli ciyaareedka oo gaabis ah, Karlsson wuxuu noqday difaaca shanaad ee taariikhda horyaalka oo ugu yaraan hal caawin ku leh 14 kulan oo isku xigta ka dib guushii 7-2 ee ka soo gaartay Edmonton Oilers 8dii Janaayo 2019. Bishii Diseembar 23, Karlsson ayaa la joojiyay markii ugu horreysay ee xirfadiisa laba ciyaarood oo loogu talagalay jeeg sharci darro ah oo loo diray madaxa ciyaaryahanka Los Angeles Kings Austin Wagner. Dhaawaca foodda ayaa sababay in Karlsson uu seego ciyaaro badan dhamaadka xilli ciyaareedka ka hor inta uusan ku soo laaban ciyaartii ugu dambeysay ee xilli ciyaareedka ee ka dhanka ah Colorado Avalanche. Waxa uu xilli ciyaareedkii ku dhameystay 45 dhibcood 53 kulan, waana dhibcaha ugu hooseeya tan iyo xilli ciyaareedkii 2012-13. Karlsson wuxuu San Jose ka caawiyay inuu gaaro Final-ka Shirka Galbeedka inta lagu gudajiray ciyaartii playoff-ka ee 2019, in kasta oo uu dhaawac kale oo lugta ah ku soo gaaray ciyaar ka dhan ah St. Louis Blues, taas oo keentay inuu ka maqnaado San Jose kulankiisii ugu dambeeyay ee playoffs-ka markii kooxdu ku lumisay 5-1 kulankii 6. Waxa uu ku dhameystay 16 dhibcood 19 kulan. 31-kii Maajo, wuxuu ku dhacay qaliin mindhicirka ah.