Tomas' second home run of the tournament gave Cuba a commanding 6-0 lead at Tokyo Dome, and the 2006 runner-up added eight runs in the sixth before the game was ended under the mercy rule.
"After losing yesterday, this was an important game for us," Tomas said. "So my three-run homer meant a lot, it brought a lot of positive energy to the team. The manager told me to sit on the outside pitch and make good contact, and I was able to do that."
Cuba will play the loser of Sunday's game between Japan and the Netherlands on Monday for a chance to advance to the March 17-19 final round in San Francisco. Taiwan is eliminated from the tournament.
A bases-clearing double by Jose Fernandez and a two-run homer by Jose Abreu highlighted the sixth in which Cuba sent 11 batters to the plate.
Cuban starter Danny Betancourt pitched six scoreless innings. Taiwanese starter Ching-Lung Lo took the loss after giving up two runs on two hits in 2-2/3 innings.
"We just didn't have to pitching tonight," Taiwan manager Chang-Heng Hsieh said. "In order to get a victory over a team like Cuba, you have to have good pitching. We got that yesterday against Japan but didn't have it tonight, and you saw what happened."
Cuba hit four home runs in the game and displays the type of power of a title contender.
"We lost yesterday, so we knew it was important to score early and keep them off the scoreboard," Cuba manager Victor Mesa said. "I reminded my players that today was an elimination game, so we needed to win."