When they were walking out to bat in front of a sparse crowd, Tamim Iqbal told Imrul Kayes what he could expect Elton Chigumbura to do with the new ball. Standard stuff, every opening pair talks to each other.

When Imrul was dropped off a full-toss and had a huge appeal turned down in the second hour, Tamim walked down the wicket and tapped the bat with his head bowed. No one could be certain if they spoke. Imrul didn't lift his bat to look for a boundary for another 25-odd overs.

Batting between 55 and 63 was a mental struggle for Tamim. He was trying too hard to force the pace a number of times. Imrul told him so, and asked him to calm down. Tamim kept hustling, and got out of the jam with a few boundaries. But he felt Imrul's support from the other end during his struggle.

Later in the day, they both acknowledged each other's reading of body language and calming effect. They said it was as important as the runs, records and milestones. It doesn't sound like a novel idea but it was mightily important for Bangladesh.

When Tamim tapped away the Zimbabwe legspinner Natsai M'shangwe for one last time before tea was called, he and Imrul had gone through two sessions untouched. Never before have a Bangladesh opening pair got through the first two sessions of a Test match. They had seen off a good start, a dropped catch, one missed review and then a long period of dominance. A string of milestones followed, but through it all their 224-run partnership was as balanced as it was rewarding for the team.

Such a start will always make the subsequent batsmen feel freer and it was evident how Mominul Haque had raced to an unbeaten 46. There was no usual pressure on the No. 3, as he had 60-odd overs of rest, a decent foundation and a bowling that had become weary by the end of the second session.

Out of the 54 times Bangladesh have batted first in a Test match, the first wicket had fallen before the tenth over on 40 occasions. If there is one particular micro-level rationale to explain Bangladesh's struggle in Test cricket, this one comes very close. When they bat first, the opening stand is broken and the opposition, of whichever quality, gets access to the top and middle-order far too quickly.

Zimbabwe had effectively a four-man attack with Chigumbura not as effective as he was in Dhaka. Tinashe Panyangara, Shingirai Masakadza and M'shangwe hardly threatened them and found little movement in the air or off the wicket. The legspinner M'shangwe created a couple of chances in the second hour but Brian Chari dropped a chance and he himself wasn't sure whether the delivery to Imrul in the 16th over would have hit the stumps. Hawk-Eye said it was going to be a plumb leg-before but the moment had passed. Zimbabwe were going to have to wait for a long time.

"We talk a lot when we bat together. When he is facing a problem, I tell him and he does too when I am batting. It does make batting easier with better communication"
Imrul Kayes on batting with Tamim Iqbal

They first put together Bangladesh's first 50-plus opening stand since last February. Then it was the first century stand since June 2010 and went past the highest Bangladeshi partnership against Zimbabwe. Soon, they recorded Bangladesh's highest opening partnership and put up the team's fourth 200-plus stand in 14 years.

Tamim said that they have always spoken to each other frankly in the middle, and understood each other's body language. They had opened for three years from 2008 to 2011, recording the previous record stand of 185 against England at Lord's, and in Chittagong became Bangladesh's most prolific partnership for any wicket.

"I have always tried talking to my opening partners and build a relation with each individual," Tamim said. "We have had a good opening stand in the past. I think we broke our previous record. We understand each other's game and we plan ahead of the game, so batting becomes easier.

"We don't think of stats when we are batting. If a partner understands your style of cricket, he can spot a rush of blood during the course of an innings. It becomes very helpful when he can calm you down. It happened when I was batting between 55 and 63. I was trying to attack too much. He calmed me down, which was helpful. I try to calm him down when he is being too excited. I enjoy batting with him."

Imrul said that they warn each other whenever they spot something worrying in their make-up, particularly when approaching a milestone and one of them is getting jittery. That happened when Tamim was two runs away from his sixth century but Imrul refused a second run as the fielder had already picked up the ball in fine leg.

"We talk a lot when we bat together," Imrul said. "When he is facing a problem, I tell him and he does too when I am batting. He was telling me how Chigumbura would bowl before we were walking in to bat. It does make batting easier with better communication.

"Tamim wanted to take a two [when he was on 98]. I told him that if you come for the second, you will be run out. It was risky for us, we can always get a single if we are at the wicket."

Imrul made a comeback in February this year when he batted at No. 3 and scored his maiden Test century against Sri Lanka, also in Chittagong. He had a mixed bag until failing in the first Test against West Indies and then missing the next one through a skin infection. He said that he needed this century to ensure he would continue to be a regular part of the Bangladesh team, and not keep making these comebacks.

"I was watching Bangladesh play quite well in this series," Imrul said. "But I didn't expect to play in this series. I knew that next time I get a chance, I can't be stable without scoring a hundred. I have to score runs. There is no alternative to scoring runs. You have to perform."

"I have been batting as an opener and one-down this year. It is slightly tricky to bat at No. 3 as an opener. You have to wait wearing your pads, which makes you uneasy. It was tough in West Indies, so I decided that next time I get a chance I will have to adjust [to a new position and the situation] even better."

Bangladesh are already 2-0 up in the series but the record-breaking opening stand has stamped their dominance over Zimbabwe until they meet again in a Test match. It was gruelling for a young team that now has to work through five more batsmen before getting into the tail. Tamim and Imrul have given the Bangladesh middle-order a chance to stretch the innings as long and wide as they want.

Mohammad Isam is ESPNcricinfo's Bangladesh correspondent. @isam84