Gary Ballance became only the second Test batsman after Kepler Wessels to score a century for two countries, hitting an unbeaten 137 for Zimbabwe against the West Indies in Bulawayo on Tuesday.Needing at least 248 runs in reply to a West Indies' declaration of 447-6 on Monday to avoid a possible follow-on, Zimbabwe declared at 379-9 after the second session on day four of the first Test.That left the hosts trailing by 68 runs after the first innings in their first Test since losing to Bangladesh two years ago.Harare-born Ballance scored four centuries for England during the last decade before returning home to make his Test debut for Zimbabwe in this match at Queens Sports Club.South Africa-born Wessels scored four centuries for Australia before returning home and making two more for his homeland when they were readmitted to Test cricket in the 1990s.Ballance and leg spinner Brandon Mavuta, who made 56 before playing across the line to a short delivery and being bowled by Jason Holder, put on 135 in a brilliant eighth-wicket stand.Aware of his key role, having come in at number five with Zimbabwe 114-3, Ballance was the epitome of caution, painstakingly building his innings.By the declaration, the 33-year-old had faced 231 balls, and his total included two sixes, one of which took him to his century and 12 fours.While Ballance was foiling West Indies' plans to bowl out Zimbabwe cheaply and force them to immediately bat again, Mavuta played a superb backup role.Having taken five West Indies wickets, he proved equally skilful with the bat and did not hold back when offered scoring chances as he slammed nine fours.The day began with Test debutant Innocent Kaia on 59, but he could add only eight more before being trapped leg