BOSTON (Reuters) - Elliott Management, Paul Singer's $35 billion hedge fund, kept up its blistering pace of pushing for corporate changes during the third quarter, outspending all rivals with campaigns at AT&T and Marathon Petroleum Corp , data released on Friday showed. The firm committed $5.2 billion in new capital during July, August and September, making it the busiest activist both by capital committed and number of campaigns launched, according to data compiled by Lazard. This year Elliott has committed $8.4 billion in 14 campaigns.