<?php
$string = '
<table border="1" cellspacing="0" cellpadding="0" style="table-layout:fixed;font-size:13px;font-family:arial,sans,sans-serif;border-collapse:collapse;border:1px solid #ccc" dir="ltr">
<colgroup>
<col width="54">
<col width="337">
<col width="233">
<col width="96">
<col width="98">
<col width="86">
</colgroup>
<tbody>
<tr style="height:18px;">
<td style="padding:0px 3px 0px 3px;vertical-align:bottom;background-color:#fff2cc;text-align:center;vertical-align:middle;border-right:;border-bottom:;">128882</td>
<td style="padding:0px 3px 0px 3px;vertical-align:bottom;background-color:#fff2cc;text-align:center;vertical-align:middle;border-right:;border-bottom:;direction:ltr;color:#000000;">Ñкономика (10-15 ÑÑÑ) </td>
<td colspan="1" rowspan="2" style="padding:0px 3px 0px 3px;vertical-align:bottom;background-color:#fff2cc;text-align:center;vertical-align:middle;border-right:;border-bottom:;direction:ltr;color:#000000;">
<span>
<div style="max-height:35px">Ðнна http://content-available-to-author-only.com/s aaa@mail.ru 2? +7(111) 111-11-11 3? --- </div>
</span>
</td>
<td style="padding:0px 3px 0px 3px;vertical-align:bottom;background-color:#fff2cc;text-align:center;vertical-align:middle;border-right:;border-bottom:;direction:ltr;color:#000000;">Ð½ÐµÐ´ÐµÐ»Ñ </td>
<td style="padding:0px 3px 0px 3px;vertical-align:bottom;background-color:#fff2cc;text-align:center;vertical-align:middle;border-right:;border-bottom:;">750</td>
<td colspan="1" rowspan="2" style="padding:0px 3px 0px 3px;vertical-align:bottom;background-color:#fff2cc;text-align:center;vertical-align:middle;border-right:;border-bottom:;direction:ltr;color:#000000;">
<span>
<div style="max-height:35px">/к</div>
</span>
</td>
</tr>
<tr style="height:18px;">
</tbody>
</table>
';
$pattern = '/<([a-z][a-z0-9]*)++(?:[^>](?=( rowspan="\d+")?))++[^>]*?(\/?)>/i';
// Важное примечание: оставит только первое вхождение rowspan
echo $result2;
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