HONG KONG, March 12 (Reuters) - Hong Kong's pro-democracy camp failed on Monday to regain some veto power in the city's legislature in a pivotal by-election, struggling to draw what they hoped would be protest votes against creeping control from Communist Party rulers in Beijing. The democrats won only two of four seats up for grabs, with the opposition now left one seat short from having the power to block most bills in the 70-seat legislative chamber. The by-election marked the first time the democratic camp has lost its long standing veto power via the ballot box, raising fresh questions over the future of the struggle for democracy and autonomy in the freest city in greater China. "The breakthrough in this by-election is a shot of confidence for our supporters and for people who hope Hong Kong can move forward and stop wasting energy with in-fighting," said Starry Lee, the leader of the city's largest pro-Beijing party, the Democratic Alliance for the Betterment and Progress of Hong Kong (DAB). The polls were triggered when six pro-democracy lawmakers were ousted from public office over invalid oaths of office in a move that critics said was politically motivated - a move that cost them their veto power. The two remaining seats have yet to be filled. Sunday's polls coincided with the historic vote in China's parliament that removed president Xi Jinping's term limits, giving him the right to stay in office indefinitely.