Smoak, who also had two homers on Monday in the United States' 11-1 rout of Netherlands Antilees, connected for a two-run homer in the third inning off Japanese starter Hiroyuki Kamegawa to help Team USA to its fifth straight victory in the tournament.
Phillies Minor Leaguer Terry Tiffee also homered in the inning to give the United States a three-run lead that was more than enough for Pirates prospect Brad Lincoln, who became the latest American to throw a gem in the tournament.
The right-hander tossed 7 1/3 innings, allowing just one run on six hits along with five strikeouts and no walks to get the win. It was just another solid outing by Team USA as its starters have combined to allow just two earned runs on 13 hits over 34 innings with 40 strikeouts.
Twins prospect Trevor Plouffe also had an RBI single to give USA a 4-0 lead in the seventh as the Americans held off a late rally by Japan to secure the win.
Chinese Taipei also extended its winning streak as it defeated Australia, 5-4, in 10 innings to win for the third straight time after starting the tournament with two consecutive losses.
Pinch-hitter Hung-Yu Lin provided the dramatics as he hit a walk-off two-run homer to lead Chinese Taipei to the victory at Antonio Casadio Stadium in Godo, Italy.
It was a wild one as the Aussies broke a 1-1 tie in the 10th by scoring three runs in the top of the inning, but Chinese Taipei answered with four runs to win it.
Both rallies were keyed by mistakes as a throwing error allowed James Bereford to score the tie-breaking run for Australia. Pirates prospect Christopher Snelling followed with an RBI single before Twins prospect Luke Hughes had a sacrifice fly to put the Aussies up, 4-1.
But Chinese Taipei rallied and scored a pair of one-out runs on a throwing error by Beresford at shortstop, and Lin followed with a pinch-hit two-run homer off Paul Mildren to give Chinese Taipei the win. The victory avenged a 5-4 loss to Australia in the first round.
The game started as a pitchers' duel between Australia's David Welch, who struck out 13 in just seven innings and allowed one run on four hits, and Chinese Taipei's Wen-Yang Liao, who went nine innings and allowed a run on four hits.
Meanwhile, rain across Italy forced three games, one from Monday and two from Tuesday, to be rescheduled for Wednesday in Italy.
Monday's Japan-Chinese Taipei game will be played Wednesday as will Tuesday's Italy-Netherlands Antilles and Mexico-Canada games. The four regularly scheduled games in the Netherlands will also be played Wednesday.
Second-round play, consisting of 16 teams, will last until Sunday. Team USA is situated in Group G, along with Italy, Australia, Canada, Chinese Taipei, Japan, Mexico and Netherlands Antilles.
The top eight teams in the second round will advance to the third and final round, which runs Sept. 22-27 exclusively in Italy.
Rhett Bollinger is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.