Having struggled to adapt to life back in the second tier over the last two seasons, Boro have enjoyed an excellent start to this campaign and knew victory over the Foxes would see them move to the summit if Southampton slipped up at Cardiff.
But, despite Saints being beaten 2-1, Tony Mowbray's side remain second on goal difference after a second home goalless draw in five days.
On a day when the headlines were dominated by Manchester City striker Carlos Tevez's refusal to go on as substitute during Tuesday night's 2-0 defeat to Bayern Munich, his City team-mate Michael Johnson - on loan at Leicester - made his first league start for three years.
The England Under-21 international was featuring in City's first team in the not too distant past, but serious injuries have limited him to infrequent appearances over the last 36 months.
Johnson made a tentative step on the road back to regular action tonight, though, replacing Gelson Fernandes in the only chance to the Foxes XI that drew with Cardiff on Sunday.
Contrasting styles were on display from the off, with Boro opting for a patient approach while the visitors were looking to utilise Jermaine Beckford and Darius Vassell with long balls over the top.
The former proved the most effective during the opening exchanges with Nicky Bailey shooting just over from range before Joe Bennett forced a smart save from Kasper Schmeichel.
It was the Foxes who has the first real opportunity, though, as Beckford nodded just over midway through the opening period.
Chances were few and far between for both sides thereafter, although Marvin Emnes threatened to liven up a drab atmosphere when forcing an excellent save from Schmeichel after dispossessing Matt Mills.
The Foxes were dealt a blow just after half-time as Beckford - a big-money deadline day signing from Everton - was forced off due to injury, Jeffrey Schlupp coming on in his place.
That change heralded a chance for the visitors when, after being cleverly found by Richie Wellens, Yuki Abe struck wide.
Seemingly awoken, Boro played with more purpose thereafter as Bennett's 20-yard effort sneaked inches past Schmeichel's post.
That was followed by an even better opportunity in the 70th minute but the hosts were again left rueing profligacy as Bailey headed wide from Barry Robson's excellent centre.
Reminding Boro of their threat, the Foxes fashioned a chance of their own soon after as Schlupp forced a smart save from Carl Ikeme.
Boro almost snatched a winner in the dying seconds but substitute Alex Nimely failed to connect with an excellent right-wing centre.
That proved the last act with Middlesbrough having to settle for a draw.