Blair will partner Glasgow youngster Ruaridh Jackson at halfback, with the 22-year-old fly-half having been given the nod ahead of his former Warriors team-mate Dan Parks.
Head coach Andy Robinson has named a near full-strength team for Saturday's fixture as Scotland build towards their huge encounters with Argentina and England.
"We have picked a strong side. There is competition for places and we could easily have picked another XV, as we did in the warm-up games," said Robinson, who hopes to mirror his previous World Cup coaching experience when he helped guide England to glory in 2003.
"Our key objective this weekend is to win the game and thus get a foothold in the tournament.
"We've trained really well in the last three months and it's now about going out and delivering."
Chris Paterson will become the first Scot to feature at four World Cups when he starts at full back having seen off the challenge of Toulon's Rory Lamont.
Test Lion Ross Ford wins his 50th cap at hooker but there is no place in the starting line up for fellow Lions Euan Murray and Nathan Hines. Hines is selected among the replacements but Murray misses out altogether.
Ali Kellock skippers the Scotland side from the second row here he is joined by Glasgow clubmate Richie Gray, while Geoff Cross betas Murray to the tight-head prop spot.
Sean Lamont starts at inside centre alongside former Northampton and now London Irish back Joe Ansbro, with Simon Danielli and Max Evans named on the wings.
After taking on the Romanians at Invercargill, Scotland have little time to relax before facing Georgia at the same venue on Wednesday.
Scotland (vs Romania, Invercargill, Saturday, 2am BST)
Chris Paterson; Max Evans, Joe Ansbro, Sean Lamont, Simon Danielli, Ruaridh Jackson, Mike Blair; Alan Jacobsen, Ross Ford, Geoff Cross, Richie Gray, Al Kellock (captain), Kelly Brown, John Barclay, Richie Vernon
Replacements: Scott Lawson, Al Dickinson, Nathan Hines, Ross Rennie, Chris Cusiter, Dan Parks, Rory Lamont
NB bold denotes Lion