When Upul Tharanga made his debut for Sri Lanka in August 2005, his was one of the more remarkable tales in international cricket. Eight months earlier, his family lost their home in the Boxing Day tsunami, that claimed thousands of lives in his home town of Ambalangoda. Only 19 then, Tharanga had played a match in Colombo the day before, and was setting out for home when he had news of the disaster. When he returned to his neighbourhood, he found "nothing was there".

Tharanga took three months' leave from the game, as he and his family began piecing their lives together, and found a friend in club teammate Kumar Sangakkara, who gave him money and equipment to help set his cricket on track again. Upon his return to the game, he caught the selectors' eye and had an international hundred one month after making his debut. Next year, five more ODI tons made him one of Sri Lanka's surest long-term prospects. Tharanga has rarely lived up to that promise since.

Serene and unyielding in full flow, but cagey and hapless all too often, few other batsmen have stretches of good form as fragile as he. Slim rewards from January's tour to Australia had him left out of the side for four months, but on his return series, Tharanga struck a scintillating 174 that raised hopes he would own Sri Lanka's troublesome second-opening spot for some time. Since that innings, he has made 7, 6, 11, 43, 3 and 5. The 43 could so easily have been 0, had he not been dropped early at second slip.

His latest innings, in the third ODI, was a fumbling, frustrating, familiar mess. Groping endlessly at balls outside off stump as the seam bowlers worked the channel, Tharanga edged a boundary between the keeper and slip, and made one run from his remaining 22 deliveries.

How blinding a difference from his innings in Kingston just over three weeks ago. That day, Tharanga caressed the ball so languidly, he seemed to be batting in slow-motion fantasy. He cut so late, yet drove and pulled so powerfully, it seemed no delivery imaginable could ever get him out. Tharanga had begun Sri Lanka's innings in a graceful trance, and finished with devilish fury, plundering 66 from his last 22 deliveries to punch out unbeaten, with a strike rate of 109.4.

Tharanga also has 13 ODI hundreds - only three fewer than Sangakkara, and Mahela Jayawardene who have both played in twice as many ODIs. How to reconcile that record with the batsman who eats up Powerplay overs, then routinely presents his wicket to slip, thanks to an incurable technical malady, which is almost untenable in the age of two new balls. This pained effort against South Africa bore a resemblance to his 20-ball torture for two runs in the 2011 World Cup final, that sucked the wind from Sri Lanka's sails and set India off apace. Some days Tharanga bats so well, his innings seem like a dream. Other times, he falls asleep at the crease.

It is a vacillating pattern he must arrest immediately, because at 28 now, and with eight years of international experience behind him, Tharanga is perfectly placed to ease the coming loss of Sri Lanka's senior batsmen. No one who sees him on his best days will doubt he is capable of greatness, yet he is now two innings away from having his place in the side roundly questioned, again. Sri Lanka have already tried two other opening combinations this year, and there are talented others in the domestic circuit capable of catching the selectors' fancy.

"We're not trying to chop and change our openers too much because we're trying to have the same combination and give the players a good run," Angelo Mathews said after the match. "Upul has shown in the recent past, when he got a big hundred, that he can bat through the innings. Unfortunately he couldn't do that in the first three matches, but I'm sure he'll come to the party in the next two.

"As batsmen we have to be consistent, and apart from TM Dilshan, Kumar Sangakkara and Mahela Jayawardene, we aren't among the runs for long. If we want to win a lot of matches in the future, we can't just leave it to the seniors. We all have to contribute."

Tharanga now approaches a fork in his career. If the inconsistency that has ruled his career so far cannot be vanquished, he may forever be banished to the cricketing purgatory so many talented men have known before, when they have flourished yearly in domestic cricket without earning a recall. But if he can discover a route to the sustained batting success he promised in his youth, Sri Lanka will be some way to solving the crisis that rushes towards them.

Andrew Fidel Fernando is ESPNcricinfo's Sri Lanka correspondent. He tweets here