During the day, the 30-share BSE Sensex rallied 777 points, driven by positive sentiment across global markets on hopes of a COVID-19 vaccine.
The index, however, made a U-turn in the last hour of trade and settled just 18.75 points, or 0.05 per cent, higher at 36,051.81.
On similar lines, the NSE Nifty closed 10.85 points, or 0.10 per cent, up at 10,618.20, after soaring 220 points during the session.
Reliance Industries (RIL) was the biggest drag on the Sensex, skidding 3.71 per cent after scaling its life-time high of Rs 1,978.50 (intra-day) as investors rushed to book profits amid a slew of announcements at its annual general meeting.
RIL Chairman Mukesh Ambani said Google will invest Rs 33,737 crore to buy 7.7 per cent stake in Jio Platforms, completing RIL's capital-raising target for the digital arm.
Ambani also announced Jio is developing a homegrown 5G telecom solution, but added that his group's planned stake sale in oil-to-chemical business to Saudi Aramco has not progressed as per the original timelines due to the COVID-19 crisis.
Bharti Airtel, ONGC, IndusInd Bank, Bajaj Finance and SBI were also among the laggards, shedding up to 4.24 per cent.
On the other hand, Infosys rallied 6.16 per cent ahead of its quarterly earnings. HCL Tech, TCS, Tech Mahindra, Axis Bank and HUL too ended with smart gains.
According to traders, during majority of the session, domestic investors were enthused by hopes of a COVID-19 vaccine as two contenders began human trials in India and one US-based candidate successfully completed the initial phase of human trials.
However, the fag-end selloff in RIL halted the rally, they said.
"The stock price of Reliance has witnessed a decline towards the end of the AGM since most of the news was already priced in and there were not many surprises," said Nirali Shah, Senior Research Analyst, Samco Securities.
Ajit Mishra, VP - Research, Religare Broking Ltd, added, "We're seeing a tussle between the bulls and bears for the last couple of sessions and we feel it would be healthy if the market witnesses some correction after the recent surge. However, the resilience of global markets would help the index to limit the downside."
BSE IT, teck, FMCG, healthcare, metal and auto indices ended up to 4.89 per cent higher, while telecom, energy, oil and gas and realty indices lost up to 3.63 per cent.
Broader BSE mid-cap and small-cap indices fell up to 0.35 per cent. World markets remained buoyant as positive results from a coronavirus vaccine trial by US-based Moderna enthused investors.
Bourses in Hong Kong, Tokyo and Seoul ended with gains, while Shanghai closed in the red.
Stock exchanges in Europe were also trading higher in opening deals.
Meanwhile, international oil benchmark Brent crude futures rose 1.10 per cent to USD 43.37 per barrel.
On the currency front, the rupee appreciated 27 paise to end at 75.15 against the US dollar.
India saw a record single-day jump of 29,429 COVID-19 cases, pushing its tally to 9,36,181 on Wednesday, while the death toll climbed to 24,309 with 582 new fatalities, according to the Union Health Ministry data. ANS ABM ABM