Leicester rescued a dramatic point four minutes into stoppage time as one goal drought ended and another continued at the King Power Stadium.
A penalty in the 94th minute by record signing Islam Slimani gave the Foxes a share of the spoils after two goals from Alvaro Negredo - his first in 12 games - looked set to heap more misery on the Premier League champions.
With the quiet Jamie Vardy’s wait for a goal extending to 15 club appearances, Leicester looked set to be sunk by Negredo’s goals on 13 and 71 minutes.
But, having levelled once from the spot through Riyad Mahrez 11 minutes before half-time, Claudio Ranieri’s men did it again at the death after Marten De Roon fouled captain Wes Morgan.
It spared Leicester a seventh defeat of the Premier League season and a miserable end to a successful week that saw them reach the last 16 of the Champions League.
Leicester’s sluggish start was punished in the 13th minute as Middlesbrough carved them open to take the lead. Negredo displayed a sure touch to control Calum Chambers’ long ball before spreading play to Gaston Ramirez wide on the left. The Spaniard then found space in the penalty area to meet Ramirez’s cross and loop a shot over Zieler and into the top corner.
Mahrez was a peripheral figure until, on the half-hour, he did superbly to create a chance for Okazaki. The Algerian produced a superb drag-back to wrongfoot Fabio and Adam Clayton before crossing for the Japan striker, who connected with a fabulous overhead kick that struck the crossbar and bounced to safety.
Four minutes later the Foxes were level from a spot-kick that Boro contested fiercely. Danny Simpson’s cross was handled by Chambers, but the on-loan Arsenal defender appeared to have been impeded by Wes Morgan a second earlier.
Mahrez stepped up and converted the penalty of the base of Valdes’s left-hand upright.
Leicester ought to have led three minutes before half-time when Okazaki created some space inside the penalty area and crossed for Vardy, but Ramirez had chased back and beat the England striker to the ball to concede a corner, although his touch just past the post gave Valdes a scare.
Leicester replaced both Mahrez and Vardy just after the hour mark with summer signings Islam Slimani and Ahmed Musa charged with adding extra impetus.
But it was Okazaki who conjured something from nothing with some clever footwork to work himself into space space on the edge of the area before his shot was saved by Valdes.
Slimani and Musa were then involved as Leicester threatened again. Slimani’s backheel found Amartey, whose lay-off was met by Musa with a shot that flew high and wide.
But on 72 minutes the visitors reclaimed the lead as they exploited a ragged Leicester rearguard.
Negredo was kept onside by Christian Fuchs and the striker met Adam Forshaw’s long pass, composed himself and beat Zieler low down.
Leicester had little answer as the absence of suspended midfielder Danny Drinkwater created a lack of creativity when they needed it most, and their frustration appeared to be complete when, in stoppage time, Amartey helped the ball wide in a goalmouth scramble, denying Slimani a clear shot at goal in the process.
But with just seconds of the added period remaining, Morgan was felled by De Roon and Slimani rifled home from the spot.
Ranieri admitted that his side were second best on the day, but insists he is not concerned about the Foxes' form.
“They played better than us. I am very happy with our character, that they believed until the end that something good could happen.
“I’m not worried [about relegation] but I'm a very pragmatic man. Now we are there, last season we were very far away but I was always watching behind me. This season we must be patient, stay together and pass the bad moment because sooner or later we will be back.”
Karanka, meanwhile, could not hide his disappointment with Boro's failure to win. “We have mixed feelings. I have feelings that I'm really proud of the players because they've played an amazing game against a team that we can't forget won the Premier League last season.
“On the other side, it's frustration as we are a newly-promoted team and for us to work for one week preparing the games, to concede the first goal as we did, it's frustrating.”
Leicester City: Zieler; Simpson, Morgan, Huth, Fuchs; Mahrez (Musa 68), Amartey, King, Albrighton; Okazaki (Gray 76), Vardy (Slimani 65).
Subs not used: Hernandez, Musa, James, Hamer, Schlupp, Gray.
Middlesbrough: Valdes; Barragan, Chambers, Gibson, Fabio; Clayton; Traore (Stuani 79), De Roon, Forshaw, Ramirez (Fischer 88); Negredo.
Subs not used: Espinosa, Leadbitter, Guzan, Downing, Nsue.Reuse content