But Argentine, Ulloa levelled just two minutes later, rising well to head in Jeffrey Schlupp's brilliant left-wing cross.
The Gunners had plenty of chances to regain the advantage, with Sanogo thwarted on numerous occasions, but they couldn't find the breakthrough and were forced to settle for a point.
The pressure will now mount for Arsene Wenger to act in the transfer market with just over 24 hours left of the window for him to sign a striker.
Arsenal kommt bei Leicester City nur zu einem Remis
PRE-MATCH - Cambiasso on the bench. Leicester are unchanged from the side that lost to Chelsea, with new signing Esteban Cambiasso on the bench. For Arsenal, there are three changes from the side that drew 2-2 with Everton last Saturday - Calum Chambers, Jack Wilshere and Alex Oxlade-Chamberlain drop out and Laurent Koscielny, Santi Cazorla and Yaya Sanogo come in. Olivier Giroud is a long term injury absentee.
20' - GOAL! LEICESTER 0-1 ARSENAL. Sanchez fires in his first PL goal after Sanogo failed to put away Cazorla's delicious scooped pass.
22' - GOAL! LEICESTER 1-1 ARSENAL Leicester are level almost immediately. Schlupp makes a great run down the left and fires over a pinpoint cross that Ulloa rises to bullet home with a fine header. 1-1.
26' - ARSENAL INJURY BLOW. Laurent Koscielny is forced to make way after initially playing on with a bandaged head. It followed an unfortunate clash with Schlupp.
49' - PENALTY SHOUT? Sanogo volleys a decent cross along the six-yard box from the right but there is no-one there to convert for the visitors. Arsenal regain possession with Sanchez on the left and Cazorla then tumbles as he tries to turn. PENALTY? There was contact but the referee says no.
53' - LEICESTER CHANCE! Ulloa finds space on the left of the area, cuts inside Chambers and then dinks the ball beyond Szczesny with a disguised attempt that floats just past the near post. Wonderful skill - but he should have scored.
57' - SAVE! Monreal powers forward down the left on the counter and slips a fine pass through for Sanogo who sees his low attempt brilliantly beaten away by Schmeichel.
61' - LEICESTER CHANCE. The hosts roar down the right through Mahrez who plays it to Ulloa in the box. The Argentine tees up Nugent but his low attempt is blocked. It looked to be heading for the far corner. Unlucky.
67' - ARSENAL CHANCE. Cazorla curls a devilish cross into the area for Sanogo, but again the striker fails to convert. It's been a bad day at the office for him.
84' - LEICESTER CHANCE. Vardy shoots... Smart save by the keeper! A lightning break by the Foxes catches Arsenal out and the substitute latches onto a pass to fizz a low shot on the run at goal. Good hands from Szczesny though.
Alexis Sanchez is the 100th different Premier League goal-scorer for Arsenal
Leicester have scored at least once in each of their last 17 league games at home.
Ulloa’s first goal in English football came against Arsenal, in a 3-2 FA Cup fourth round loss with Brighton.
Leicester’s goal was the first time Arsenal conceded to a promoted team in the PL in six, since a 4-1 win at home to Reading on 30 March 2013.
Arsenal have only won three of their last 10 Premier League away games (D2 L4).
Arsenal are now unbeaten for eight PL matches – this is their best unbeaten run since December – January of last season, also eight. They fail to beat a promoted side for the first time in eight matches (1-1 at Southampton on 1 Jan 2013).
(Stats courtesy of Opta and Infostrada)
Alexis Sanchez scores for Arsenal at Leicester (Reuters)
Will Arsenal bring in a striker? The Gunners had countless attempts and carved out a number of good openings but couldn't turn them into goals. Sanogo is a raw talent but he wasted a number of opportunities to win this. Arsenal must bring someone in over the next 24 hours if they are to be serious challengers for the title. Olivier Giroud's injury surely makes it of paramount importance.
MAN OF THE MATCH
Leonardo Ulloa (Leicester). Continued his impressive start to life in the topflight with a second goal in three outings. Showed Arsenal's strikers how to do it with an energetic display capped by a priceless equaliser.
Leicester: Schmeichel 7, De Laet 7, Morgan 8, Moore 7, Konchesky 7, Mahrez 7, King 7, Hammond 7, Schlupp 7, Nugent 6, Ulloa 8. Subs: Albrighton 6, Vardy 6, Drinkwater 6.
Arsenal: Szczesny 6, Debuchy 6, Mertesacker 6, Koscielny 5, Monreal 6, Flamini 6, Ramsey 7, Cazorla 6, Ozil 5, Alexis 7, Sanogo 5. Subs: Chambers 6, Podolski 5, Oxlade-Chamberlain 5.
THE MATCH IN A TWEET
- Sports & Recreation
- Leonardo Ulloa
- Yaya Sanogo
- Premier League
- Alexis Sanchez
- Santi Cazorla
- Jeffrey Schlupp
- Wojciech Szczesny
- Laurent Koscielny
- Calum Chambers