(Reuters) – Microsoft Corp is expected to surpass Yahoo Inc for the first time in the $140.2 billion worldwide digital advertising market, according to estimates by research firm eMarketer released on Tuesday. Microsofts global ad revenue share for 2014 is forecast at 2.54 percent, edging ahead of Yahoos 2.52 percent share. Google Inc will remain No. 1 with a 31.54 percent share, trailed by Facebook Inc with 7.79 percent, the research firm said. Facebook and Twitter are expected to have the largest gains in market share, with Facebook rising from 5.82 percent in 2013 while Twitter Incs share should grow to 0.79 percent this year from 0.5 percent in 2013.