To extract multiple items from text using a single regular expression, create a regular expression with named patterns, for example, IPAddr, Day, etc. (see below). The Discard named pattern specifies items that are not used. Then use the Regex Match property to extract the item corresponding to the named pattern from the results:

String Pattern = @"(?<IPAddr>[\S]+)(?<Discard>[\s-\[]*)(?<Day>\d{1,2})(?<Discard>/)(?<Month>[a-zA-Z]+)(?<Discard>/)(?<Year>\d{2,4})(?<Discard>:)(?<Hour>\d{1,2})(?<Discard>:)(?<Minute>\d{1,2})(?<Discard>:)(?<Second>\d{1,2})(?<Discard>[\s]*)(?<TZInt>[\+\-]*\d{2})(?<TZFrac>\d{2})(?<Discard>([\]\s])*""(GET|HEAD)([\s])*)(?<File>[\S]*)(?<Discard>[^""]*""[\s]*)(?<Status>[0-9]*)(?<Discard>[\s]*)(?<Bytes>([0-9])*)(?<Discard>[^""]*"")(?<RefURL>[^""]*)(?<Discard>[^""]*""[^""]*"")(?<UserAgent>[^""]*)";
Regex RE = new Regex(Pattern, RegexOptions.IgnoreCase | RegexOptions.Compiled);
Regex RE = new Regex(Pattern, RegexOptions.IgnoreCase | RegexOptions.Compiled);
...
String Line = SR.ReadLine().Trim();
...
Match M = RE.Match(Line);

Item.IPAddress = M.Result("${IPAddr}");
int Day = Int32.Parse(M.Result("${Day}"));