Scotland's hopes of qualifying for Smith's goal in the 0 win over Liechtenstein in Group I play.
The result leaves Scotland in second place, one point clear of third-place Czech Republic, with the Scots facing a trip to Spain on the final day of qualifying on Tuesday while the Czech Republic visits Lithuania.
Following Spain's 2-0 win over the Czechs on Friday, Scotland took the field on Saturday knowing that a win would move the team into second in the group.
The visitors came out strong, and after Steven Naismith missed a pair of decent chances to put Scotland in front, Mackail-Smith eased some nerves by sending a looping header over goalkeeper Peter Jehle and into the Liechtenstein net from 10 yards.
Scotland had the better of the play in the second half as well but was unable to tally a second goal, which made for some nervous moments at the end of the game but ultimately saw the team secure three crucial points.