US STOCKS-Wall St extends bounce-back; S&P above key levels

* Apple (NasdaqGS: AAPL - news) rallies, lifting S&P 500 and Nasdaq

* S&P 500 back above 14-day moving average

* Indexes up: Dow 1.14 pct, S&P 1.67 pct, Nasdaq 2.02 pct

By Yasmeen Abutaleb

NEW YORK, Oct 21 (Reuters) - U.S. stocks rallied on Tuesday, with the S&P 500 on track for a fourth straight session of gains boosted by strong corporate results, including Apple's.

The S&P 500 and Dow Jones were up more than 1 percent while the Nasdaq rose more than 2 percent, boosted by better-than-expected results from several major tech companies.

The S&P 500 has gained more than 6 percent from its session low last Wednesday, when the benchmark was down nearly 10 percent from its intraday record. The index is on track to close above its 14-day moving average for the first time since Sept. 24 and was also trading above its 200-day average.

At 1:55 p.m., the Dow Jones industrial average rose 187.14 points, or 1.14 percent, to 16,586.81, the S&P 500 gained 31.81 points, or 1.67 percent, to 1,935.82 and the Nasdaq Composite added 87.12 points, or 2.02 percent, to 4,403.19.

Apple Inc rose 2.5 percent to $102.28 a day after revenue topped expectations, helped by strong iPhone sales. It also gave a strong outlook for the holiday quarter.

The largest percentage gainer and decliner on the S&P 500 were both related to earnings. The largest gainer was Waters Corp, which rose 8.8 percent, while the largest decliner was Chipotle, down 6.1 percent.

The largest gainer on the Nasdaq 100 was Illumina Inc (NasdaqGS: ILMN - news) , which rose 9 percent, while the largest decliner was Mattel Inc (NasdaqGS: MAT - news) , down only 0.4 percent.

While earnings have largely come in strong so far this quarter, concerns continue to swirl over the pace of global economic growth. China's gross domestic product grew 7.3 percent in the third quarter, the slowest pace since the first quarter of 2009.

U.S. existing home sales rose 2.4 percent in September, above expectations, hitting their highest level in a year.

Advancing issues outnumbered declining ones on the NYSE by 2,490 to 559, for a 4.45-to-1 ratio on the upside; on the Nasdaq, 1,886 issues rose and 739 fell for a 2.55-to-1 ratio favoring advancers.

The S&P 500 index was posting 21 new 52-week highs and 1 new low; the Nasdaq Composite was recording 40 new highs and 25 new lows. (Reporting by Yasmeen Abutaleb; Editing by Nick Zieminski)