In a see-saw trade, the index slipped into the negative territory but recovered and was up 120 points at 25,862 points at 0945 hrs.
At the same time, the Nifty of the National Stock Exchange rose by 38.60 points to 7,847.60 after dipping to a low of 7,801 in early trade.
The Sensex had opened strong by 383 points and the Nifty recaptured 7,900 level in early trade on across the sector value-buying by participants even as Chinese markets continued to slide.
Brokers said emergence of buying at prevailing lower levels in bluechips coupled with covering-up of short positions by speculators, helped key indices to trade in the positive zone.
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Besides, a recovery at other Asian markets influenced sentiments here, they said.
The Sensex had crashed by 1,624.51 points -- its biggest single-day fall.
Among other Asian markets, Hong Kong's Hang Seng was up 1.36 per cent, while Japan's Nikkei was up by 1.10 per cent in early trade.
However, Shanghai Composite index tumbled 4.49 per cent.
The US Dow Jones Industrial Average ended 3.57 per cent lower in yesterday's trade.