如何从API检索的json中提取信息

我试图从API获取一些信息，但总是失败。API代码：

{"matches":[{"matchId":2032325149,"region":"EUW","platformId":"EUW1","matchMode":"CLASSIC","matchType":"MATCHED_GAME","matchCreation":1427400448291,"matchDuration":2225,"queueType":"RANKED_SOLO_5x5","mapId":11,"season":"SEASON2015","matchVersion":"5.6.0.190","participants":[{"teamId":100,"spell1Id":3,"spell2Id":4,"championId":53,"highestAchievedSeasonTier":"UNRANKED","timeline":{"creepsPerMinDeltas":{"zeroToTen":0.9,"tenToTwenty":0.9,"twentyToThirty":0.6,"thirtyToEnd":1.2},"xpPerMinDeltas":{"zeroToTen":253.60000000000002,"tenToTwenty":237.8,"twentyToThirty":477.29999999999995,"thirtyToEnd":448.4},"goldPerMinDeltas":{"zeroToTen":128.2,"tenToTwenty":169.6,"twentyToThirty":310.9,"thirtyToEnd":211.2},"csDiffPerMinDeltas":{"zeroToTen":-0.8,"tenToTwenty":-0.5499999999999998,"twentyToThirty":-1.2499999999999998,"thirtyToEnd":-0.30000000000000027},"xpDiffPerMinDeltas":{"zeroToTen":-12.299999999999983,"tenToTwenty":-127.04999999999998,"twentyToThirty":120.09999999999997,"thirtyToEnd":-491.9},"damageTakenPerMinDeltas":{"zeroToTen":187.2,"tenToTwenty":644.0999999999999,"twentyToThirty":1015.2,"thirtyToEnd":2076.2},"damageTakenDiffPerMinDeltas":{"zeroToTen":9.149999999999963,"tenToTwenty":32.49999999999997,"twentyToThirty":126.24999999999991,"thirtyToEnd":762.9000000000001},"role":"DUO_SUPPORT","lane":"BOTTOM"},"masteries":[{"masteryId":4211,"rank":2},{"masteryId":4213,"rank":2},{"masteryId":4221,"rank":1},{"masteryId":4222,"rank":3},{"masteryId":4232,"rank":1},{"masteryId":4233,"rank":3},{"masteryId":4234,"rank":3},{"masteryId":4244,"rank":1},{"masteryId":4312,"rank":3},{"masteryId":4313,"rank":3},{"masteryId":4322,"rank":1},{"masteryId":4324,"rank":1},{"masteryId":4331,"rank":3},{"masteryId":4334,"rank":1},{"masteryId":4341,"rank":1},{"masteryId":4342,"rank":1}],"stats":{"winner":false,"champLevel":15,"item0":2049,"item1":3401,"item2":3270,"item3":2010,"item4":3110,"item5":3082,"item6":3340,"kills":1,"doubleKills":0,"tripleKills":0,"quadraKills":0,"pentaKills":0,"unrealKills":0,"largestKillingSpree":0,"deaths":11,"assists":10,"totalDamageDealt":31311,"totalDamageDealtToChampions":9198,"totalDamageTaken":31747,"largestCriticalStrike":0,"totalHeal":3600,"minionsKilled":36,"neutralMinionsKilled":0,"neutralMinionsKilledTeamJungle":0,"neutralMinionsKilledEnemyJungle":0,"goldEarned":8264,"goldSpent":8055,"combatPlayerScore":0,"objectivePlayerScore":0,"totalPlayerScore":0,"totalScoreRank":0,"magicDamageDealtToChampions":7159,"physicalDamageDealtToChampions":2038,"trueDamageDealtToChampions":0,"visionWardsBoughtInGame":0,"sightWardsBoughtInGame":0,"magicDamageDealt":22000,"physicalDamageDealt":5572,"trueDamageDealt":3737,"magicDamageTaken":15037,"physicalDamageTaken":16608,"trueDamageTaken":102,"firstBloodKill":false,"firstBloodAssist":false,"firstTowerKill":false,"firstTowerAssist":false,"firstInhibitorKill":false,"firstInhibitorAssist":false,"inhibitorKills":0,"towerKills":0,"wardsPlaced":28,"wardsKilled":1,"largestMultiKill":1,"killingSprees":0,"totalUnitsHealed":4,"totalTimeCrowdControlDealt":445},"participantId":0,"runes":[{"runeId":5273,"rank":9},{"runeId":5289,"rank":9},{"runeId":5317,"rank":9},{"runeId":5357,"rank":3}]}],"participantIdentities":[{"participantId":0,"player":{"summonerId":66366116,"summonerName":"name","matchHistoryUri":"/v1/stats/player_history/EUW1/217404427","profileIcon":690}}]}]}

我正在尝试获取"Kills"值，这是我的php代码：

        <?php   
    $result = file_get_contents('API URL LINK HERE);
    $key = json_decode($result);
        print '<p><b>' . $key->matches->participants->stats->Kills . '</b></p>';
?>

有人能纠正我的代码吗？非常感谢。