By Benjamin Pimentel, MarketWatch SAN FRANCISCO (MarketWatch) -- Shares of Akamai Technologies Inc. tumbled Thursday, after the company issued a muted forecast, but the tech sector rallied to push the Nasdaq Composite Index into positive territory. Akamai (AKAM) fell 14.7% to close at $34.94, the leading decliner on the S&P 500 Index. However, the S&P 500 (SPX) rose 0.4% to close at 1,360, , thanks to gains in shares of Citrix Systems Inc. (CTXS) which jumped 9.7% to close at $85.37 after the information-technology-services company reported upbeat results. Citrix was one of the S&P 500's top gainers. "Guidance appears conservative and we see upside to estimates in the second half of 2011," said Lazard Capital Markets analyst Joel Fishbein said in a note. "Customer activity and pipeline are at record levels, and Citrix continues to have good momentum on the back of strong execution." The Nasdaq Composite Index (RIXF) edged higher by 0.1% to close at 2,873. But the Morgan Stanley High Tech 35 Index (MSH) was down 0.4%, while the Philadelphia Semiconductor Index (SOX) slid 0.7%. The tech sector also took a hit from shares of Teradyne Inc. (TER), which were down 12.4% to close at $16.03 a day after the electronic production equipment maker reported a jump in quarterly profit, but issued a weaker-than-expected forecast.