Mayne, who kicked 37.12 last season, entered the derby under growing pressure to perform after booting just two goals from his opening five games.
The 188cm forward responded by kicking the second goal of the match, before being swung onto Darling when defender Zac Dawson injured his ankle in the second quarter.
Match Report: Fremantle v West Coast
Darling finished the match with just two goals from 14 possessions, with Mayne keeping a tight check on the star forward.
Dawson is unlikely to recover in time for Saturday's clash with Port Adelaide at Adelaide Oval, while fellow defender Luke McPharlin is also in some doubt after injuring his thigh early in the derby.
Although Alex Silvagni is a strong chance to replace Dawson, Lyon flagged the possibility of Mayne playing in defence against the Power.
And with promising young forwards Matt Taberner and Michael Apeness on Freo's list, Lyon said Mayne may find himself in defence more often.
"We like the flexibility of it," Lyon said.
Ross Lyon post-match Q&A: Round 7
Midfielder Stephen Hill (hamstring) is set to return against the Power, while fellow onballer David Mundy is free to play after accepting a reprimand for his block on Eagles tagger Scott Selwood.
Port Adelaide is riding high in second spot following a four-game winning run, with forward Jay Schulz leading the Coleman Medal race with 24 goals.
The Power are set to be bolstered by the returns of Hamish Hartlett and Alipate Carlile, who missed last week's win over GWS due to gastro.
