The visitors were in front after only four minutes when Marlon King cut out a poor Neil Clement pass and played in Williams for the opener.

Johnson doubled the lead in injury-time when he drilled in a low shot to end his injury-plagued season on a high.

Albion rarely threatened but when they did Paul Gerrard was on hand to deny Lee Hughes and Thomas Gaardsoe.

Gary Megson's West Brom side have disappointed since securing promotion and the last thing they needed was Clement to present Forest with a gilt-edged early opportunity.

Williams needed no second invitation when one-on-one with Russell Hoult.

Johnson went close and Alan Rogers forced Hoult into a save low to his left before Albion had their first effort on goal, a fierce drive by Sean Gregan.

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It failed to ignite the hosts, although after a cheeky effort from halfway by Andy Reid, they finally hit their stride.

Forest goalkeeper Gerrard denied Hughes, with a reaction save from close range, and Gaardsoe before half-time.

And Gerrard was forced to save at the feet of James Chambers after the break.

Artim Sakiri also went close with a free-kick, Dobie headed over and Sakiri wasted a golden opportunity when he shinned a Hughes cross over the bar.

And after withstanding the pressure Forest broke to cap their season with a stunning strike from Johnson with time running out.

West Brom: Hoult, Chambers, Moore, Gaardsoe, Robinson (Dyer 82), O'Connor (Sakiri 55), Gregan, Koumas, Clement, Hughes, Hulse (Dobie 61).
Subs Not Used: Murphy, Haas.

Nottm Forest: Gerrard, Impey (Louis-Jean 55), Walker, Dawson, Rogers, Jess, Evans, Williams, Reid, Johnson, King.
Subs Not Used: Roche, Doig, Westcarr, Sonner.

Attendance: 26,821

Referee: D Gallagher (Oxfordshire).