Virender Sehwag's brilliant batting gave India the advantage after they restricted South Africa to 305 in the first innings on day two of the second Test at the Eden Gardens in Kolkata on Monday.
At close of play, India were 129 for the loss of opener Gautam Gambhir's wicket.
Sehwag, 82, looked set to reach his ninth Test century. Rahul Dravid was unbeaten on a solid 33.
Earlier, the Indian bowlers shared the spoils in the morning session and took wickets at regular intervals to make short work of the South African innings.
Zaheer Khan and Irfan Pathan claimed three wickets each, Harbhajan Singh two while Sourav Ganguly and Anil Kumble claimed one each.
Morning session:
The day did not start well for South Africa. The visitors lost the wicket of Zander De Bruyn after just three runs were added to the overnight total of 227.
The cool morning resulted in some moisture in the air and Zaheer Khan exploited it to the maximum by getting De Bruyn (15) to edge one to wicketkeeper Dinesh Karthik, who claimed his fourth catch of the innings. (230 for 6)
South Africa's approach to batting hasn't done them any favours. When you score at a slow pace you are always in the danger of capitulating quickly with too little on board. In India, wickets tend to fall in a heap or not at all.
South Africa's run-rate at this point was 2.57. With six batsmen back in the pavilion, one hoped that Kallis would start playing a few strokes.
But that didn't happen. Instead, what did happen was that Sourav Ganguly introduced himself back into the attack. It was an inspired move, though at that point one did not think so.
Kallis and Shaun Pollock, the new batsman, played out a few overs -- 15 to be precise. They put on exactly 31 runs, played a few strokes but did nothing to force the Indians to do anything different.
Then, Ganguly, who till this point was content bowling out-swingers, bowled a beauty to Kallis to get his wicket. The ball pitched way outside the off-stump and swung in. Kallis shouldered arms and the ball did enough to clip the top of middle stump. (261 for 7)
The ball was a beauty and there is no denying that, but Ganguly was helped by the defensive approach. If Kallis had played shots, he might have got around 30-odd runs more, but he was gone for 121 after facing 259 balls and spending what seemed an eternity at the crease.
The partnership was worth 31 but the South Africans were now in danger of handing the match on a platter to the Indians.
Pollock was joined by Justin Ontong, a player who started out as a batsman but is now an erratic leg-spinner.
Five overs after Kallis's dismissal, Pollock was gone as well and South Africa were tottering. Anil Kumble got his first wicket of the match, the 432nd of his career, and went past Richard Hadlee in the all-time wicket-takers' list.
The ball in question jumped and bounced on Pollock, who could do little but fend at it. The resultant edge went straight to Rahul Dravid, who made no mistake. (273 for 8)
Thami Tsolekile, the South African wicketkeeper, strode out to the wicket. The best South Africa was hoping for on day 2 was scoring 350 and then getting some quick wickets.
Ontong (16) and Tsolekile (3) played sensibly till the umpires called lunch after 111 overs were bowled in the innings. The visitors had reached 289 for 8.
The innings could have well been over had Karthik held on to two catches off Kumble in the overs before lunch. The young 'keeper has looked at home against the pacemen but his keeping to the spinners is a different matter altogether.
Ganguly bowled a brilliant spell and ended the session with figures of 9-3-14-1.
India dominated the first session. Zaheer, Ganguly and Kumble claimed a wicket each to put India in the driver's seat.
Post-lunch session
It took only six balls from Harbhajan Singh after lunch to end the South African resistance. The off-spinner was kept out of the attack throughout the morning session because of the regular fall of wickets to the other bowlers, but he got his chance and wasted no time in getting into the thick of action.
Tsolekile (15 off 53 balls) lobbed the first ball, a full-toss, straight back to Harbhajan, who completed an easy caught and bowled dismissal. (305 for 9)
Mahkaya Ntini (0) defended one ball before he played a typical tail-ender's shot to the mid-off region, where Pathan took a good catch over his head. South Africa were all out for 305.
Ontong was not out on 16.
South Africa were well short of their intended target of around 400, which gives India a chance to put together a good first innings total and take the match by the scruff of its neck.
India innings
With only 305 runs on the board, Graeme Smith knew he had to attack and get as many Indian wickets with the new ball. And if one of those dismissed happened to be Virender Sehwag it would be a huge bonus.
With three slips and a gully, Smith certainly had the right intentions and he got an early reward for positive thinking when Gautam Gambhir, who scored 96 in the last Test, was dismissed by Pollock in the seventh over of the innings.
Gambhir (7 off 22 balls) goes across his stumps a lot and that makes him a prime candidate for a leg-before decision. That's exactly the weakness Pollock exploited and trapped the left-hander in front. (17 for 1)
Dravid walked in and from ball one looked more positive than he has in a very long time. Sehwag, at the other end, was content to wait for the bad ball, and when he did get it made sure he got the maximum.
Another plus for India is that as long as Sehwag is at the wicket, the run-rate is never a problem.
At tea, after 14 overs India had reached 48 for 1, with Sehwag unbeaten on 26 off 41 and Dravid on 10 off 22.
Post-tea session
The Indians consolidated after tea as Sehwag and Dravid were content biding their time at the wicket and allowing the bowlers tire themselves. But soon they launched into a fierce counter-attack that left all those watching gasping for breath.
The first 17 overs of the session saw nothing extraordinary happen as the batsmen scored only 37 runs during that period. Sehwag reached his eighth fifty in Test cricket and his first at the Eden Gardens, off 79 balls.
Then the run-rate of the innings, which had been steadily dropping, shot up in the space of four overs.
It all started in one Ontong over. A huge appeal for leg before wicket, off the second ball, against Sehwag was turned down by the umpire. That provided a spark in Sehwag. The next ball was smashed through the covers for four; the ball after that was a full-toss and was hit over the mid-wicket boundary for a six; the fifth ball was short and pulled to the mid-wicket boundary for another four.
The South African skipper got together with his bowler and tried to formulate a strategy to keep Sehwag quiet for the last ball of the over. Ontong came round the wicket and pitched the ball outside the leg-stump. Sehwag was expecting it and reverse-swept to the backward point boundary. This was what people had come to watch at the Eden Gardens.
21 runs were scored off the next three overs. The first 17 yielded 37, but 40 runs came in super-quick time in the next four overs.
It was the perfect session for India and watching Sehwag on fire seemed to inspire Dravid as well. The India vice-captain came out of his shell and played a few shots.
Play ended early again due to bad light. The umpires offered the light to the batsmen, who, after a 112-run partnership for the second wicket, had no hesitation in accepting the offer.
Sehwag was unbeaten on 82 off 107 balls, including 11 boundaries and a six, while Dravid was not out on a patient 33 off 106 balls.
At close of play, India trail by 176 runs and will be looking to hammer in the advantage on day three. For that to happen, Sehwag will need to stay in the middle for as long as possible, because right now no one seems to have an answer to his brilliance.
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